Average Actual Evapotranspiration Research Articles

Intercomparison of multisource actual evapotranspiration satellite products in Bilate watershed, Ethiopia

Recent advancements in satellite remote sensing have led to increased spatial and temporal resolution of actual evapotranspiration (AET) estimates across scales. Yet, the accuracy of AET products remains unknown for many regions, prompting further investigation to guide selection. This study intercompares five AET products within Ethiopia’s Bilate watershed, focusing on the 2009-2018 period. The products assessed include TerraClimate, Food and Agriculture Organization Water Productivity (FAO WaPOR), Moderate Resolution Imaging Spectroradiometer Operational Simplified Surface Energy Balance (ModisSSEBop), and Synthesis of Global AET. Reference evapotranspiration estimated using ground station climate data served as a basis for comparing the Satellite Products (SP). The intercomparison was conducted using descriptive statistics, scatter plots and Pearson’s Correlation Coefficient to assess correlation, standard deviation, and root mean square error. Additional error statistics were also considered. Findings reveal higher AET values in the highlands compared to the lowlands of the Bilate watershed. A weak correlation (<0.35) exists between ETo and satellite-derived AET, potentially due to the averaging of AET values across diverse land cover classes, contrasting with point-scale reference measurements. The variance among AET products was varied across seasons and elevation ranges. While the annual patterns of AET were consistent across the products, large discrepancies in magnitude (average AET varies from 25 to 83 mm per month in the lower part) were detected. The ModisSSEBop global and continental products showed minimal mismatches, whereas the Synthesis of Global and FAO WaPOR products displayed slight differences. Notably, the FAO WaPOR’s AET estimates showed relatively closer agreement with many products in terms of magnitude and variability of AET. In conclusion, the study highlights significant random and systematic differences between the AET products. The substantial mismatch between the products underscores the necessity for continued research to refine AET product accuracy through improved input dataset and revisiting the algorithms.

Evapotranspiration fusion and attribution analysis in the upper and middle reaches of the Yellow River Basin

Study regionThe Upper and Middle Reaches of the Yellow River Basin Study focusTaking the upper and middle reaches of the Yellow River as the research area, 15 types of models developed by the fusion of four multi-source products of GLDAS-Noah V2.1, ERA5-Land, GLEAM v3.6a and GLEAM v3.6b were assessed. Based on the fusion results of actual evapotranspiration(ET), the key factors that drive the spatial variation in actual evapotranspiration was explored, the land surface parameters of Fu formula in different watersheds were estimated, the relationship between land surface parameters and ecological construction measures was established, and the contribution rate of precipitation, potential evapotranspiration, NDVI and check-dam control area to ET change was quantified. New hydrological insights for the regionThe multi-year average actual evapotranspiration from 2003 to 2018 in the watersheds controlled by Tangnaihai, Lanzhou, Toudaoguai, Longmen and Tongguan is 378, 368, 346, 368 and 410 mm/year, respectively. The optimal fusion of the actual evapotranspiration is employing the Extreme Learning Machine to fuse the GLDAS-Noah V2.1 and GLEAM v3.6b products. The long-term actual evapotranspiration estimated from the Fu formula incorporating the ecological construction measures have high agreement with the fusion results. The impact of soil moisture on the spatial variation of actual evapotranspiration is significant. The contribution rate of precipitation to ET change is the highest, followed by NDVI, potential evapotranspiration and check-dam control area.

Water Balance Trends along Climatic Variations in the Mediterranean Basin over the Past Decades

The heterogeneous ecosystems in the Mediterranean Basin (MB) are becoming sensitive to water stress. To investigate the climatic stress, a water budget study was conducted over the basin using TerraClimate simulations for a long temporal range (1990–2020). According to the budget accounting, forested regions received the highest precipitation (P) on average compared to other land use types (annual mean ≈633 mm yr−1), and even then, they were in a water deficit state (−0.42 mm yr−1). Tree plantations in North Africa (Libya and Morocco) were also in a water deficit state; however, their average P was very low (≈12 mm yr−1) compared to that of northern parts of the MB, and the average Actual Evapotranspiration (AET) was ≈15 mm yr−1. Also, the water balance in other land use systems (rain-fed, irrigated croplands, and rangelands) was either negative or near zero. As a whole, the basin’s average annual P was ≈538 mm yr−1, the annual average AET was ≈415 mm yr−1, and the runoff (Q) was equivalent to 123 mm yr−1, which shows a strong influence of ET over the region. Since runoff was negligible in most dry areas, the AET’s large contribution was notable in the North African base of the Atlas Mountains including the Nile delta region. This indicates that precipitation and evaporation are the principal mechanisms of the water balance in the MB. The result shows strong climate variability over Southern Europe, Turkey, and the western Balkans in the recent years, affecting the AET and making their land use systems more vulnerable to water stress. This benchmark study signifies the consistent need for water storage in the Mediterranean vegetation systems of the basin. It also indicates two distinct climate clusters for water balance modeling.

Effects of landscape conservation on the ecohydrological and water quality functions and services and their driving factors

Since the implementation of landscape conservation of the green heart area in the Changsha-Zhuzhou-Xiangtan Metropolitan Region, the landscape structure and pattern have changed significantly. The ecosystem service functions in the area have been improved, but the status of ecohydrological and water quality and service functions (EHWQSFs) is still unclear. To clarify the status of EHWQSFs and their driving factors influenced by landscape conservation, this study analysed landscape changes using remote sensing image data from 1998, 2008, and 2018 and the changes and their spatial characteristics using the Soil and Water Assessment Tool (SWAT) and spatial analysis methods. The results showed that the dominant land types in the area were forestland and cropland from 1998 to 2018; the area of forestland and construction land expanded and that of cropland decreased year by year; the annual average surface runoff volume rose, and the annual average actual evapotranspiration and soil water content fell from 1998 to 2008 and rose from 2008 to 2018; and all pollutant indicators decreased significantly after 2008. The areas with higher surface runoff were mainly concentrated in the central and southern regions, those with higher evapotranspiration were in the northwestern and southwestern regions, those with higher soil water content were in the northern region, and those with higher sediment and nitrogen and phosphorus pollutant contents were in the central and southeastern regions. The results showed that land use, land cover and meteorological factors were the most significant drivers on EHWQSFs and illustrated that EHWQSFs in the area decreased after 1998. There was a significant improvement after 2008 and the area currently has a good status. This study not only provides insights into land use, land cover and meteorological factors that have significant impacts on EHWQSFs but also highlights that the landscape conservation of the area can improve ecosystem service functions.

Effects of global climate change on the hydrological cycle and crop growth under heavily irrigated management – A comparison between CMIP5 and CMIP6

Quantifying the impact of global climate change on the water cycle and crop production is essential for water resource management and agricultural production planning. This study compared multiple GCM (General Circulation Model) projections of CMIP5 (Coupled Model Intercomparison Project 5) and CMIP6 and further used the selected GCMs to quantify the impact of future climate change on hydrology and crop production under intensive irrigation management in the North China Plain using an improved SWAT model (SWAT-MAD). Taylor’s skill score was used firstly to screen out six groups of GCMs with better simulation performance from 10 pairs of homologous GCMs of CMIP5 and CMIP6. The selected GCMs of CMIP5 and CMIP6 were further used to drive SWAT-MAD for a robust evaluation of climate change impacts. Results showed that during winter wheat growing season, average actual evapotranspiration (ETa) increased by 3%, 3%, 4%, and 5%, respectively, under 2041–2070 RCP4.5, 2041–2070 SSP2-4.5, 2041–2100 RCP4.5, and 2071–2100 SSP2-4.5 scenarios, compared to the historical period (1971–2000). During summer maize growing season, those changes in ETa were 4%, 2%, −0.2%, and −3%. Predicted future precipitation, air temperatures, and surface runoff could increase, while irrigation could decrease as precipitation increased. The dynamic patterns of leaf area index of winter wheat and summer maize indicated that there is a tendency for early emergence and maturity of both crops in the future, and the daily total biomass elevated with a corresponding increase in final yields. The highest increases in yields of winter wheat and summer maize were 18.9% and 16.7%. The findings not only contribute to enhancing the confidence of future projections using CMIP6 but also facilitate our understanding of the relative uncertainty of GCMs. This study provides technical and data support for pre-selections of GCMs and decision making in best management practices for groundwater conservation and agricultural production.

InVEST model-based estimation of water yield in the Upper Tuul river basin

The estimation and mapping of water yield are of significant importance to the effective planning and management of water resources in Mongolia. In this study, we quantified and assessed the water yield of the Upper Tuul River basin using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Water yield model. The study aimed to test whether it is possible to estimate the water yield of the selected research area using the model. The required input data included land use and land cover, mean annual precipitation and potential evapotranspiration, soil depth, and plant available water content. In addition, those data were obtained from Landsat 8, Climate Hazards Group Infrared Precipitation with Station data (CHIRPS), MODIS Global Terrestrial Evapotranspiration Product (MOD16), and International Soil Reference and Information Centre (ISRIC) database. Finally, we generated spatial distribution maps, namely, mean actual evapotranspiration (mm), mean water yield (mm), and the volume of water yield (km3) by pixel within the research area. According to the modelling results, the estimated value for mean annual precipitation was 295.08 mm, and 827.09 mm respectively for potential evapotranspiration, 229.13 mm for average actual evapotranspiration, 55.89 mm and 0.43 km3 for water yield within the study area. The result was slightly higher (15.1 mm) in terms of mean actual evapotranspiration compared to the results of previous studies, conducted in the same research area, and it was found that the potential water yield in the study area has also been impacted. However, the InVEST (Water Yield) model can be used for future research studies concerning water yield and resource in river basins as it is possible to further improve the model results by using in-situ measurement data and satellite products with high spatial accuracy as input data.

Global Evapotranspiration Datasets Assessment Using Water Balance in South America

Evapotranspiration (ET) connects the land to the atmosphere, linking water, energy, and carbon cycles. ET is an essential climate variable with a fundamental importance, and accurate assessments of the spatiotemporal trends and variability in ET are needed from regional to continental scales. This study compared eight global actual ET datasets (ETgl) and the average actual ET ensemble (ETens) based on remote sensing, climate reanalysis, land-surface, and biophysical models to ET computed from basin-scale water balance (ETwb) in South America on monthly time scale. The 50 small-to-large basins covered major rivers and different biomes and climate types. We also examined the magnitude, seasonality, and interannual variability of ET, comparing ETgl and ETens with ETwb. Global ET datasets were evaluated between 2003 and 2014 from the following datasets: Breathing Earth System Simulator (BESS), ECMWF Reanalysis 5 (ERA5), Global Land Data Assimilation System (GLDAS), Global Land Evaporation Amsterdam Model (GLEAM), MOD16, Penman–Monteith–Leuning (PML), Operational Simplified Surface Energy Balance (SSEBop) and Terra Climate. By using ETwb as a basis for comparison, correlation coefficients ranged from 0.45 (SSEBop) to 0.60 (ETens), and RMSE ranged from 35.6 (ETens) to 40.5 mm·month−1 (MOD16). Overall, ETgl estimates ranged from 0 to 150 mm·month−1 in most basins in South America, while ETwb estimates showed maximum rates up to 250 mm·month−1. ETgl varied by hydroclimatic regions: (i) basins located in humid climates with low seasonality in precipitation, including the Amazon, Uruguay, and South Atlantic basins, yielded weak correlation coefficients between monthly ETgl and ETwb, and (ii) tropical and semiarid basins (areas where precipitation demonstrates a strong seasonality, as in the São Francisco, Northeast Atlantic, Paraná/Paraguay, and Tocantins basins) yielded moderate-to-strong correlation coefficients. An assessment of the interannual variability demonstrated a disagreement between ETgl and ETwb in the humid tropics (in the Amazon), with ETgl showing a wide range of interannual variability. However, in tropical, subtropical, and semiarid climates, including the Tocantins, São Francisco, Paraná, Paraguay, Uruguay, and Atlantic basins (Northeast, East, and South), we found a stronger agreement between ETgl and ETwb for interannual variability. Assessing ET datasets enables the understanding of land–atmosphere exchanges in South America, to improvement of ET estimation and monitoring for water management.

Remote sensing assessment of available green water to increase crop production in seasonal floodplain wetlands of sub-Saharan Africa

Producing more food for a growing population requires sustainable crop intensification and diversification, particularly in high-potential areas such as the seasonal floodplain wetlands of sub-Saharan Africa (SSA). With emerging water shortages and concerns for conserving these multi-functional wetlands, a further expansion of the cropland area must be avoided as it would entail increased use of blue water for irrigation and infringe on valuable protected areas. We advocate an efficient use of the prevailing green water on the existing cropland areas, where small-scale farmers grow a single crop of rainfed lowland rice during the wet season. However, soil moisture at the onset of the rains (pre-rice niche) and residual soil moisture after rice harvest (post-rice niche) may suffice to cultivate short-cycled crops. We developed a methodological approach to analyze the potential for green water cultivation in the pre- and post-rice niches in the Kilombero Valley Floodplain in Tanzania, as a representative case for seasonal floodplain wetlands in SSA. The three-step approach used open-access remote sensing datasets to: (i) extract cropland areas; (ii) analyze soil moisture conditions using evaporative stress indices to identify the pre- and post-rice niches; and (iii) quantify the green water availability in the identified niches through actual evapotranspiration (AET).We identified distinct patterns of green water being available both before and after the rice-growing period. Based on the analyses of evaporative stress indices, the pre-rice niche tends to be longer (~70 days with average AET of 20–40 mm/10-day) but also more variable (inter-annual variability >30%) than the post-rice niche (~65 days with average AET of 10–30 mm/10-day, inter-annual variability <15%). These findings show the large potential for cultivating short-cycled crops beyond the rice-growing period, such as green manure, vegetables, maize, and forage legumes, by shifting a portion of the nonproductive AET flows (i.e., soil evaporation) to productive flows in form of crop transpiration. A cropland area of 1452 to 1637 km2 (53–60% of the total cropland area identified of 2730 km2) could be cultivated using available green water in the dry season, which shows the significance of such change for food security, livelihoods, and resilience of the agricultural community in Kilombero. A wider application of the developed approach in this study can help identifying opportunities and guiding interventions and investments towards establishing sustainable intensification and diversification practices in floodplain wetlands in SSA.

Developing a pan-European high-resolution groundwater recharge map – Combining satellite data and national survey data using machine learning

Groundwater recharge quantification is essential for sustainable groundwater resources management, but typically limited to local and regional scale estimates. A high-resolution (1 km × 1 km) dataset consisting of long-term average actual evapotranspiration, effective precipitation, a groundwater recharge coefficient, and the resulting groundwater recharge map has been created for all of Europe using a variety of pan-European and seven national gridded datasets. As an initial step, the approach developed for continental scale mapping consists of a merged estimate of actual evapotranspiration originating from satellite data and the vegetation controlled Budyko approach to subsequently estimate effective precipitation. Secondly, a machine learning model based on the Random Forest regressor was developed for mapping groundwater recharge coefficients, using a range of covariates related to geology, soil, topography and climate. A common feature of the approach is the validation and training against effective precipitation, recharge coefficients and groundwater recharge from seven national gridded datasets covering the UK, Ireland, Finland, Denmark, the Netherlands, France and Spain, representing a wide range of climatic and hydrogeological conditions across Europe. The groundwater recharge map provides harmonised high-resolution estimates across Europe and locally relevant estimates for areas where this information is otherwise not available, while being consistent with the existing national gridded datasets. The Pan-European groundwater recharge pattern compares well with results from the global hydrological model PCR-GLOBWB 2. At country scale, the results were compared to a German recharge map showing great similarity. The full dataset of long-term average actual evapotranspiration, effective precipitation, recharge coefficients and groundwater recharge is available through the EuroGeoSurveys' open access European Geological Data Infrastructure (EGDI).

Predicting long-term hydrological change caused by climate shifting in the 21st century in the headwater area of the Yellow River Basin

The Qinghai-Tibetan Plateau (QTP) is one of the amplifiers of global climate change. The headwater area of the Yellow River Basin (HYRB) on the QTP is the dominant water source region for the whole Yellow River Basin. However, the sensitive responses of hydrological processes to the intensifying climate change are exerting high uncertainties to the water cycle in the HYRB. The aim of this study was to investigate the potential climate change under three Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5) and their hydrological impacts in this region using the ensemble climate data from eight general circulation models (GCMs) and the Soil and Water Assessment Tool (SWAT). Compared to the baseline (1976–2015), the projected climate indicated a rise of 7.3–7.8% in annual precipitation, 1.3–1.9 °C in maximum air temperature, and 1.2–1.8 °C in minimum air temperature during the near future period (2020–2059), and an increment of 9.0–17.9%, 1.5–4.5 °C, and 1.3–4.5 °C in precipitation, maximum and minimum temperature, respectively, during the far future period (2060–2099). The well-simulated SWAT modeling results suggested that due to a wetter and warmer climate, annual average actual evapotranspiration (AET) would increase obviously in the future (31.9–35.3% during the near future and 33.5–54.3% during the far future), which might cause a slight decrease in soil water. Water yield would decrease by 16.5–20.1% during the near future period, implying a worsening water crisis in the future. Till the end of this century, driven by the increased precipitation, water yield would no longer continue to decrease, with a decline by 15–19.5%. Overall, this study can not only provide scientific understanding of the hydrological responses to the future climate in both semi-arid and alpine areas, but also contribute to the decision support for sustainable development of water resources and protection of eco-environment in the HYRB.

A trait‐based approach to assessing resistance and resilience to wildfire in two iconic North American conifers

Abstract Ongoing changes in fire regimes have the potential to drive widespread shifts in Earth's vegetation. Plant traits and vital rates provide insight into vulnerability to fire‐driven vegetation shifts because they can be indicators of the ability of individuals to survive fire (resistance) and populations to persist (resilience) following fire. In 15 study sites spanning climatic gradients in the southern Rocky Mountains, USA, we quantified variation in key traits and vital rates of two co‐occurring, widely distributed conifers (Pinus ponderosa Douglas ex. P. Lawson &amp; C. Lawson and Pseudotsuga menziesii (Mirb.) Franco). We used mixed‐effects models to explain inter‐ and intraspecific variation in tree growth, survival, bark thickness and seed cone production, as a function of species, tree life stage (i.e. diameter, height and age), average climate, local competition and site conditions. Pinus ponderosa was predicted to survive low‐severity fire at a 23% earlier age than P. menziesii. Pinus ponderosa had thicker bark and more rapid juvenile height growth, traits conferring greater fire resistance. In contrast, P. menziesii was predicted to produce seed cones at a 28% earlier age than P. ponderosa. For both species, larger individuals were more likely to survive fire and to produce cones. For P. ponderosa, cone production increased where average actual evapotranspiration (AET) was higher and local competition was lower. More frequent cone production on productive sites with higher AET is an important and underappreciated mechanism that may help to explain greater resilience to fire in these areas. Synthesis. Our analyses indicated that many plant traits and vital rates related to fire differed between Pinus ponderosa and Pseudotsuga menziesii, with trade‐offs between investment in traits that promote individual defence to fire and those that promote recolonization of disturbed sites. Future changes in fire regimes will act as a filter throughout North American forests, with our findings helping to infer which individuals and populations of two iconic species are most vulnerable to future change and offering a framework for future inquiry in other forests facing an uncertain future.

Limitations to recovery following wildfire in dry forests of southern Colorado and northern New Mexico, USA.

Climate warming is contributing to increases in wildfire activity throughout the western United States, leading to potentially long-lasting shifts in vegetation. The response of forest ecosystems to wildfire is thus a crucial indicator of future vegetation trajectories, and these responses are contingent upon factors such as seed availability, interannual climate variability, average climate, and other components of the physical environment. To better understand variation in resilience to wildfire across vulnerable dry forests, we surveyed conifer seedling densities in 15 recent (1988-2010) wildfires and characterized temporal variation in seed cone production and seedling establishment. We then predicted postfire seedling densities at a 30-m resolution within each fire perimeter using downscaled climate data, monthly water balance models, and maps of surviving forest cover. Widespread ponderosa pine (Pinus ponderosa) seed cone production occurred at least twice following each fire surveyed, and pulses of conifer seedling establishment coincided with years of above-average moisture availability. Ponderosa pine and Douglas-fir (Pseudotsuga menziesii) seedling densities were higher on more mesic sites and adjacent to surviving trees, though there were also important interspecific differences, likely attributable to drought and shade tolerance. We estimated that postfire seedling densities in 42% (for ponderosa pine) and 69% (for Douglas-fir) of the total burned area were below the lowest reported historical tree densities in these forests. Spatial models demonstrated that an absence of mature conifers (particularly in the interior of large, high-severity patches) limited seedling densities in many areas, but 30-yr average actual evapotranspiration and climatic water deficit limited densities on marginal sites. A better understanding of the limitations to postfire forest recovery will refine models of vegetation dynamics and will help to improve strategies of adaptation to a warming climate and shifting fire activity.

Climatic variability on groundwater recharge of Mymensingh district in Bangladesh

A study was carried out in Mymensingh sadar upazila of Bangladesh in order to evaluate the effects of climatic variability on groundwater (GW) recharge and evapotranspiration (ET) over the period of 2006 - 2015. The annual GW recharge was computed by using soil moisture balance method, while CROPWAT-8.0 model was used to determine potential evapotranspiration (PET) and Grindley method was also used to estimate actual evapotranspiration (AET). In the case study area, the average temperature and rainfall showed no trend (almost constant), whereas humidity showed a declining trend over the study period. Analysis of rainfall trend revealed that there was considerable increase in annual rainfall with a mean of 2125 mm found over the study period. Groundwater recharge showed an increasing trend over the whole period, and the maximum recharge of 247.86 mm found in 2013, while maximum GW depletion of 136.8 mm found in 2014. In case of annual PET, the maximum of 1403.76 mm found in 2006, whereas the minimum of 1115.76 mm found in 2013. The AET showed a slightly declining trend over the 10 years of study, and the highest average AET of 1014.24 mm observed in 2007, whereas the lowest of 772.92 mm was in 2013. There was no significant relationship among groundwater recharge and annual variability of average temperature, and average rainfall found while only the annual variability of average humidity was found to be inversely related with groundwater recharge.&#x0D; Progressive Agriculture 30 (1): 104-112, 2019

三北工程黄土高原丘陵沟壑区森林降温增湿效果研究

PDF HTML阅读 XML下载 导出引用 引用提醒 三北工程黄土高原丘陵沟壑区森林降温增湿效果研究 DOI: 10.5846/stxb201812282830 作者: 作者单位: 中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,北京林业大学自然保护区学院,中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划课题（2016YFC0503706，2016YFC0503403）；中国科学院科技服务网络计划项目资助（KFJ-STS-RKT-005）；中国科学院A类战略性先导科技专项资助（XDA20020402） The cooling and humidifying effect by the forest ecosystem in the hilly and gully area of Loess Plateau of the Three North Shelter Forest System Project region Author: Affiliation: Institute of Geographical Sciences and Natural Resources Research,Institute of Geographical Sciences and Natural Resources Research,Institute of Geographical Sciences and Natural Resources Research,School of Conservation, Beijing Forestry University,Institute of Geographical Sciences and Natural Resources Research Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生态系统可通过植被蒸腾与土壤蒸发作用调节区域温度与湿度。三北工程黄土高原丘陵沟壑区属于干旱和半干旱区，森林降温增湿功能有助于改善区域生存环境。在分析研究区森林覆被变化基础上，利用Penman-Monteith公式模拟了森林实际蒸散量，研究了森林增湿与降温效果。研究结果显示：（1）1980-2015年研究区森林面积增加了2.25%，主要来自荒草地、耕地和荒漠；（2）1980-2015年研究区森林6-9月实际蒸散总量为1.19×1010-1.40×1010 t/a，平均实际蒸散量为219-257 mm，可使区域6-9月绝对湿度每日增加0.47-0.55 g/m3，相对湿度每日增加2.87%-3.32%；（3）森林通过蒸散作用吸热量为29.15×1015-34.26×1015 kJ/a，单位面积蒸散吸热量为53.72×108-63.13×108 kJ hm-2 a-1，通过蒸散吸热日降温量为0.92-1.08℃/d；（4）研究区森林蒸散量在1980-2010年逐渐增加，但在2015年明显下降，这主要是由降水减少导致；森林面积较大的山西和陕西森林蒸散降温增湿效果较好。通过对比相同年份不同土地覆被发现，森林实际蒸散量显著高于其他土地覆被类型。因此，未来研究区可在水资源承载能力范围内适当增加森林面积，充分发挥森林调节区域气候的作用。 Abstract:The ecosystem can regulate regional temperature and humidity through evapotranspiration. The climate in the hilly and gully area of the Loess Plateau in the Three North Shelter Forest System Project (TNSFSP) region is arid and semi-arid, and the cooling and humidifying function of the forest ecosystem is crucial for improving the living environment in this region. Based on the analysis of forest cover changes in this area, in this study, we simulated using the Penman-Monteith formula and investigated the contribution of evapotranspiration by ecosystems to regional climate regulation. The results show that:(1) The forest area in the study region (mainly grassland, cropland, and desert) increased by 2.25% from 1980 to 2015. (2) The total amount of forest actual evapotranspiration (AET) in the study area from 1980 to 2015 was between 1.19×1010 t/a and 1.40×1010 t/a, and average AET ranged from 219 mm to 257 mm. Absolute humidity from June to September in 1980 to 2015 increased by 0.47-0.55 g/m3 per day, and the relative humidity will increase by 2.87%-3.32% per day. (3) Heat absorption of the forest through evapotranspiration was estimated as 29.15×1015 to 34.26×1015 kJ/a, evapotranspiration per hectare was 53.72×108-63.13×108 kJ hm-2 a-1), and the daily cooling rate by evapotranspiration was 0.92-1.08℃ d-1. (4) The amount of forest evapotranspiration increased gradually from 1980 to 2010, but it decreased significantly in 2015, which was mainly caused by the decrease in precipitation. Spatially, forests in Shanxi and Shaanxi provinces, with a larger forest area, had better evapotranspiration and humidification effects. Comparison of the different land cover in 1980 to 2015 showed that the actual evapotranspiration of the forest was still significantly higher than other land cover types. In future, the forest area will be appropriately increased within the carrying capacity of water resources, and the role of forest will be even more crucial in regional climate regulation. 参考文献 相似文献 引证文献

Estimation of Actual Evapotranspiration Distribution in the Huaihe River Upstream Basin Based on the Generalized Complementary Principle

The accurate estimation of actual evapotranspiration can help improve the utilization of water resources and ease the ecological stress. Based on the generalized complementary principle proposed by Brutsaert in 2015, we used meteorological and hydrological data to estimate the actual evapotranspiration at a resolution of 1 km × 1 km between the years of 1961 and 2000 and also verified the model’s stability. In this study, we used the water balance equation to calibrate the parameters, coupled with the spatial simulation results of the meteorological elements in the actual evapotranspiration model. The estimation results of actual evapotranspiration show that the generalized complementary principle model had high estimation precision in this basin, with an average absolute error of 16.64 mm and an average relative error of 2.25%. With respect to spatial distribution, the average actual evapotranspiration over the years in the basin tended to have high and low distribution in the northern and southern parts of the basin, respectively. The actual evapotranspiration in the basin showed a decreasing trend over the period, with a rate of 24.1 mm/10 years. Correlation coefficient analysis showed that the percentage decreases in percentage sunshine and the decreases in the daily range of temperature were the main reasons for the decrease in actual evapotranspiration.

High resolution water body mapping for SWAT evaporative modelling in the Upper Oconee watershed of Georgia, USA

AbstractTechnological improvements in remote sensing and geographic information systems have demonstrated the abundance of artificially constructed water bodies across the landscape. Although research has shown the ubiquity of small ponds globally, and in the southeastern United States in particular, their cumulative impact in terms of evaporative alteration is less well quantified. The objectives of this study are to examine the hydrologic and evaporative importance of small artificial water bodies in the Upper Oconee watershed in the northern Georgia Piedmont, USA, by mapping their locations and modelling these small reservoirs using the Soil Water Assessment Tool. Comparative Soil Water Assessment Tool models were run with and without the inclusion of small reservoir surface area and volume. The models used meteorological inputs from 1990–2013 to represent years with drought, high precipitation, and moderate precipitation for both the calibration and evaluation periods. Statistical comparison of streamflow indicated that the calibration methodology produced results where the default model simulation without reservoirs fit observed flows more closely than the modified model with small reservoirs included (e.g., Nash–Sutcliffe efficiency of 0.72 vs. 0.64, r2 of 0.73 vs. 0.66, and percent bias of 11.4 vs. 21.6). In addition, Penman–Monteith, Hargreaves, and Priestley–Taylor evapotranspiration equations were used to estimate actual evaporation from 2,219 small water bodies identified throughout the 1,936.8 km2 watershed. Depending on the evaporation equation used, water bodies evaporated an average of 0.03–0.036 km3/year for the period 2003–2013. Using Penman–Monteith further, if the reservoirs were not considered and average actual evapotranspiration rates from the rest of the basin were applied, only 0.016 km3 of water would have left the basin as a result of evapotranspiration. This finding suggests construction of small reservoirs increased evaporation by an average of 0.017 km3 per year (approximately 46,500 m3/day). As the construction of small reservoirs continues and high resolution image data used to map these water bodies becomes increasingly available, watershed models that evolve to address the cumulative impacts of small water bodies on evaporation and other hydrologic processes will have greater potential to benefit the water resource management community.

Determination of water-yield basil function under deficit irrigation conditions and use of nano fertilizer

Basil (Ocimum basilicum L.) is one of the important aromatic plants belonging to the family Lamiaceae, which is used as an herb, spice as well as fresh vegetable.The present study was performed to determine the irrigation depth index under different management conditions with evaluating the effect of deficit irrigation, soil texture and nano fertilization on basil. The experiment was performed as a factorial based on randomized complete block design (RCBD) with 18 treatments and three replications at weather station, Ferdowsi University of Mashhad. Deficit irrigation treatments consisted of three levels of irrigation (I1=100% ETc), (I2=75% ETc), (I3=50%ETc) and three levels of nano fertilizers, containing nano fertilizer with full concentration (F1), 70% (F2), and nonusing of nano fertilizer (F3) were implemented in two light soil texture (S1) and medium soil texture (S2). The results showed that the average actual evapotranspiration estimation by REC-P55 device has been equal to 3.38 mm at the beginning of the growing period of basil, which amount has increased to 8.60 mm during basil development in the middle of growth period. The results of crop coefficient analysis showed that the maximum kc of basil (1.42) was detected in July. The results also indicated that the highest water use efficiency (WUE) was obtained in terms of fresh and dry herb yield as 2.06 and 0.37 kg/m3 in S2I3F3 treatment, respectively, while the maximum water use efficiency in terms of seed yield (0.37 kg/m3) was obtained in S1I2F2 treatment. Using the research results, according to different levels of water use of functions of yield Y(w), cost C(w), and benefit B(w) for basil based on mathematical and economic analysis of these functions, irrigation index and optimal irrigation depths were evaluated. It was found that with deficit irrigation under water restriction conditions, with the aim of maximum use of water volume unit, the optimal water consumption depth will be reduced by 20% compared to maximum irrigation mode. Also, with this amount of deficit irrigation, the maximum Rial return per cubic meter of water consumption would be as 1849 Rials.

Applicability of established drought index in Huang-Huai-Hai region based on actual evapotranspiration.

Based on the modeled products of actual evapotranspiration with NOAH land surface model, the temporal and spatial variations of actual evapotranspiration were analyzed for the Huang-Huai-Hai region in 2002-2010. In the meantime, the agricultural drought index, namely, drought severity index (DSI) was constructed, incorporated with products of MOD17 potential evapotranspiration and MOD13 NDVI. Furthermore, the applicability of established DSI in this region in the whole year of 2002 was investigated based on the Palmer drought severity index (PDSI), the yield reduction rate of winter wheat, and drought severity data. The results showed that the annual average actual evapotranspiration within the survey region increased from the northwest to the southeast, with the maximum of 800-900 mm in the southeast and the minimum less than 300 mm in the northwest. The DSI and PDSI had positive correlation (R2=0.61) and high concordance in change trend. They all got the low point (-0.61 and -1.33) in 2002 and reached the peak (0.81 and 0.92) in 2003. The correlation between DSI and yield reduction rate of winter wheat (R2=0.43) was more significant than that between PDSI and yield reduction rate of winter wheat (R2=0.06). So, the DSI reflected a high spatial resolution of drought pattern and could reflect the region agricultural drought severity and intensity more accurately.

Effect of diversified crop rotations on groundwater levels and crop water productivity in the North China Plain

Water shortage is the major bottleneck that limits sustainable yield of agriculture in the North China Plain. Due to the over-exploitation of groundwater for irrigating the winter wheat–summer maize double cropping systems, a groundwater crisis is becoming increasingly serious. To help identify more efficient and sustainable utilization of the limited water resources, the water consumption and water use efficiency of five irrigated cropping systems were calculated and the effect of cropping systems on groundwater table changes was estimated based on a long term field experiment from 2003 to 2013 in the North China Plain interpreted using a soil–water-balance model. The five cropping systems included sweet potato→cotton→sweet potato→winter wheat–summer maize (SpCSpWS, 4-year cycle), ryegrass–cotton→peanuts→winter wheat–summer maize (RCPWS, 3-year cycle), peanuts→winter wheat–summer maize (PWS, 2-year cycle), winter wheat–summer maize (WS, 1-year cycle), and continuous cotton (Cont C). The five cropping systems had a wide range of annual average actual evapotranspiration (ETa): Cont C (533mm/year)<SpCSpWS (556mm/year)<PWS (615mm/year)<RCPWS (650mm/year)<WS rotation (734mm/year). The sequence of the simulated annual average groundwater decline due to the five cropping systems was WS (1.1m/year)>RCPWS (0.7m/year)>PWS (0.6m/year)>SPCSPWS and Cont C (0.4m/year). The annual average economic output water use efficiency (WUEe) increased in the order SpCSpWS (11.6yuan¥m−3)>RCPWS (9.0¥m−3)>PWS (7.3¥m−3)>WS (6.8¥m−3)>Cont C (5.6¥m−3) from 2003 to 2013. Results strongly suggest that diversifying crop rotations could play a critically important role in mitigating the over-exploitation of the groundwater, while ensuring the food security or boosting the income of farmers in the North China Plain.

The differences of water balance components of Caragana korshinkii grown in homogeneous and layered soils in the desert–Loess Plateau transition zone

Soil texture greatly influences soil water movement, thus may affect the water balance and vegetation growth in the desert–Loess Plateau transition zone. This study is to determine if the water balance differs in homogeneous and layered soils with Caragana korshinkii stands in semiarid region. Soil water measurements up to 500-cm depth were taken in 2006 and 2007 on homogeneous sandy soil, homogeneous silt loam soil, and layered soil with sand overlying silt loam. HYDRUS-1D was used to simulate the soil water balance. The results indicated the annual water balance components were greatly affected by soil layering. The ratio of average actual evapotranspiration (ETa) to precipitation (P) during the two years in the layered soil was slightly lower than that in homogeneous soils. The ratios of annual actual transpiration (Tr) to evapotranspiration were 50.9%, 41.2% and 30.6% in layered soil, homogeneous sandy soil, and homogeneous silt loam soil, respectively. C. korshinkii grown in layered soil had deeper soil water recharge and higher Tr/ETa ratio, thus had more available water for transpiration than that in homogeneous soils. This study suggested the layered soil with sand overlying silt loam is more favorable to C. korshinkii growth in terms of water use than homogeneous soils in the desert–Loess Plateau transition zone.