Changes In Evapotranspiration Research Articles

Impact of Climate Change on the Development of Viticulture in Central Poland: Autoregression Modeling SAT Indicator

Ongoing climate change is having a profound impact on agriculture, which is attracting attention from the scientific community. One of its effects is an increase in average temperature, which is a key factor in grape cultivation. This may increase the popularity of viticulture in central Europe. The aim of this study was to assess the potential for the development of viticulture in central Poland based on SAT changes from 1975 to 2021, in addition to changes in evapotranspiration, occurrence of late spring and early autumn frosts and frosty days in selected years from this period as an important factors relating to climate change. The research utilized data obtained from the Institute of Meteorology and Water Management—National Research Institute. The Bai–Perron test was used to determine the direction of temperature changes. An AR(1) autoregression model was used to predict SAT changes in central Poland for the years 2022–2026, based on the results of the Bai–Perron test. As part of the in-depth research on the SAT index, reference evapotranspiration calculations were also made as a second factor that is considered an important indicator of climate change. The Sum of Active Temperatures from 1975 to 2021 in the provinces of central Poland showed an increasing trend of 0.07% per year. The average SAT in central Poland in 2022–2026 is expected to range from 2700 °C to 2760 °C. Considering the current thermal conditions in central Poland and the forecasts for the coming years, it can be expected that vineyard cultivation will develop in this region. However, the research shows that the observed increasing trend in evapotranspiration, both in total in individual years and in the period of the greatest vegetation, i.e., in the months from May to the end of August, will result in an increasing need in central Poland to ensure adequate irrigation in developing vineyards.

A causal physics-informed deep learning formulation for groundwater flow modeling and climate change effect analysis

In this study, we propose and test a formulation for building causal physics-informed hybrid models over traditional physics-informed hybrid models (H-HBVo) and a convolutional neural network (1D-CNN) in groundwater level (GWL) modeling. Two types of models are built based on our formulation and named H-HBV and H-Lin, because they integrate two different hydrological models. The comparison is made in terms of performance and ability to learn cause-and-effect relationships between inputs and outputs. The novelty of this study lies in the CRC (Causal Relationship Constraints) conditions, derived from a mathematical development, that are imposed on the layers of the physics-informed hybrid model to force it to learn causal relationships. The results showed that the 1D-CNN algorithm performed slightly better than the hybrid algorithms, and that the H-Lin and H-HBV algorithms together achieved slightly better results than the traditional hybrid algorithm, H-HBVo. It is also obtained that the algorithms subjected to our formulations (H-Lin and H-HBV) are the ones with satisfactory causality properties and that the integration of domain knowledge is not sufficient to obtain causal and interpretable models within the framework of hybrid algorithms. Subsequently, an analysis of the effect of climate change is carried out for Quebec (Canada) using H-HBV models. The results show that the RCP and SSP scenarios give fairly similar results, i.e. an increase in GWL between 2011 and 2090 with median amplitudes varying between + 5.6 and + 7 cm. In some cases, the amplitude of increase can exceed between + 14 and + 23 cm, and even reach between + 35 and + 70 cm. The results of the climate change analysis are consistent with changes in vertical inflow and potential evapotranspiration, the input variables, for the different climate scenarios, confirming the robustness of our formulation.

Global evapotranspiration from high-elevation mountains has decreased significantly at a rate of 3.923 %/a over the last 22 years

Clarifying the responses of human activities and climate change to the water cycle under variable environments is crucial for accurately assessing regional water balance. An analysis of the changes in actual evapotranspiration and its driving factors was conducted in the global high-elevation mountains during the period from 2001 to 2022. Utilizing 18 formulas for calculating evapotranspiration, which are based on comprehensive, temperature, radiation, and mass transfer, and then simulated the variations in reference evapotranspiration. Furthermore, we optimized the ET simulation model based on the most effective simulation results and projected future changes using scenario simulation data. Our findings reveal that: 1) ET at high-elevation mountains has significantly decreased at an average rate of 3.923 %/a, with monthly values ranging from 31.179 to 33.652 mm and an average of 32.646 mm; 2) The radiation-based model of Irmark-Allen is particularly well-suited for simulating ET at high-elevation mountains, with precision analysis and the Taylor diagram confirming its superior simulation performance. After optimizing the model using the method of least squares, the value of R2 before and after the optimization were 0.633 and 0.853, respectively. 3) An upward trend in ET under both SSP245 and SSP585 scenario in future simulation projections. Attribution analysis has identified Vapor Pressure Deficit as the key positive driver influencing the change of ET in global high-elevation mountains. Structural equation modeling further reveals that variations in net radiation and precipitation play a significant role in altering evapotranspiration rates. Meanwhile，The water balance analysis reveals that ET has been declining from 2001 to 2022. This phenomenon can be largely attributed to the substantial decline in vapor pressure deficit, the rise in the Normalized Difference Vegetation Index signifying increased vegetation cover, and the reduction in shallow soil moisture during the same period. These factors collectively explain the notable decrease in ET observed in high-elevation mountains.

Enhanced evapotranspiration induced by vegetation restoration may pose water resource risks under climate change in the Yellow River Basin

Quantifying the impacts of climate change, vegetation greening and human activities (CVH) on evapotranspiration (ET), surface drought intensity (ET divided by precipitation, SDI), and vegetation available water (precipitation minus ET, VAW) would improve our understanding of water cycle processes. The Yellow River Basin (YRB) is a significant climate-sensitive region in China, resulting in an obvious spatiotemporal heterogeneity of ET, SDI, and VAW in response to driving variables. In this study, we analysed the spatiotemporal variation characteristics of ET, SDI, and VAW in the YRB from 1984 to 2018. We also quantified the direct and indirect contributions of the CVH to the changes in ET, SDI, and VAW, and revealed the influence mechanism of each link. Finally, water resource risks were assessed from a probabilistic perspective. The results indicated that vegetation greening was the primary driver of ET with an increase rate of 1.60 mm/a, which was also the most important influencing factor of SDI increase and VAW decrease. Leaf area index (LAI) and relative humidity (RH) jointly dominated the ET changes in 66 % of the YRB, temperature (Temp) dominated the SDI changes in nearly half of the basin, precipitation (Pre) and LAI jointly dominated the VAW changes in 66 % of the YRB. Temp indirectly influenced ET primarily through LAI, whereas LAI primarily influenced ET directly. Temp had a significant direct impact on SDI, while LAI mainly influenced SDI through RH and wind speed (WS). Temp exhibited the most substantial negative influence on VAW. LAI was identified as the primary factor contributing to water resource risks, with a probability reaching 0.8, while the probabilities associated with other factors inducing such risks were similar at the basin level, but disparities existed among different land use types. The findings of the study significantly enhanced our understanding of the role that the CVH played in hydrological processes, serving as a crucial foundation for achieving a balance between ecological restoration and socio-economic development in the YRB.

Contribution of climatic variables and their interactions to reference evapotranspiration changes considering freeze-thaw cycles in the Tibetan Plateau during 1960–2022

While the direct impact of climate change on reference evapotranspiration (ET0) has been extensively studied, there is limited research on the indirect impact resulting from the interaction between climatic variables. This gap hinders a comprehensive understanding of climate change effects on ET0. Additionally, there is scarce exploration into the quantitative effect of freeze-thaw cycles on ET0 variation. In this study, we employed path analysis and dependent variable variance decomposition methods to discern the direct and interactive effects of climatic variables on ET0 in the Tibetan Plateau from 1960 to 2022. Annual ET0 exhibited variation across basins, with the coefficient of variability during the thawed period smaller than that during the non-thawed period. On an annual scale, the largest contribution to ET0 variation came from water vapor pressure deficit (VPD) at 47.7%. This contribution was amplified by its coupled interaction with temperature (T) at 47.1%, although the contribution was partially offset by the interactive effects of VPD with downward shortwave radiation and wind speed at −2.4% and − 27.6%, respectively. During different freezing-thawing periods, VPD primarily controlled ET0 variation, with its interaction with other climatic variables enhancing its impact. Furthermore, soil moisture, influenced by freeze-thaw cycles, exhibited a strong correlation with T and VPD, indicating the significant effect of freeze-thaw cycles on ET0 variation. The weak correlation between ET0 and NDVI suggested that vegetation growth had a limited regulatory effect on ET0. These findings provide valuable insights into the impact of interactions between climatic variables on hydrological processes, enhancing our understanding of the interactive roles of hydrometeorological variables.

Revisiting the contribution of different factors in determining the changes in potential evapotranspiration over China.

In this paper, a daily gridded observation data across China from 1961 to 2022 were used to calculate daily potential evapotranspiration (PET). The observed variables included daily temperature, sunshine hours, average wind speed, and average relative humidity. PET was determined using the Penman-Monteith method recommended by the Food and Agriculture Organization (FAO). The long-term trend of PET was investigated in six regions of China during different seasons. To further compressed the influence of various meteorological factors on the PET trend, the contribution of each meteorological element to the long-term trend of PET was analyzed. The results indicate the following: (1) PET reaches its peak during summer which values from 145 to 640 mm, while it is lowest during winter from 21 to 244 mm. (2) The spatial patterns of PET trend changes are relatively similar across the four seasons, characterized by a decrease in the eastern regions and an increase in the western regions. The reduction is most significant during the summer and the range of trend is from -2.04 to 1.48 mm/day, while the increase becomes more pronounced in the winter which trend is from -0.34 to 0.53 mm/day. (3) The contribution of factors varies significantly across different regions. In spring and autumn, RH and U have little difference in contribution from other factors. But tsun is varies different from regions, the contribution value is largest in the northwest and smallest in the northeast. However, during summer, tsun become the most significant contributor in the YZ and SE regions, while in winter, Tm emerges as the most significant contributor to the PET trend in all six subregions. In SW, the contribution from U2 is the smallest in all seasons, with RH and Tm being the two crucial factors determining the PET trend in this region.

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.

Indigenous lands and conservation units slow down non-GHG climate change in the Cerrado-Amazon ecotone

Preserving tropical forests by avoiding deforestation and forest degradation is essential for maintaining ecosystem services. Brazilian Conservation Units (CUs) and Indigenous Lands (ILs) have effectively prevented deforestation and supported climate regulation. However, these protected areas face increasing threats from forest fires and droughts across the Amazon and Cerrado biomes. This study assesses how disturbances affect climate regulating factors (surface temperature (LST), evapotranspiration (ET), and albedo) in Mato Grosso state, among different land uses (CUs, ILs, and multiple-use areas - MUs). To do so, we analyzed satellite data collected between 2001 and 2020. Results showed that MUs (outside protected areas) had lower ET (∼10%), higher daytime LST (∼1.5 °C), and higher albedo (∼10%) than CUs and ILs in both biomes in 2001. Over the study period, MUs experienced a greater increase in LST (Amazon: ∼1.4 °C; Cerrado: ∼1.1 °C) and albedo (Amazon: ∼6%; Cerrado: ∼3%) compared to protected areas, regardless of the biome. In contrast, ILs and CUs showed smaller mean changes in LST (∼0.2 °C), ET (∼1.3%), and albedo (∼1.3%). These changes were associated with native vegetation loss, forest fires, and water stress. Our results highlight the important role of protected areas in maintaining climate stability, with higher ET, lower LST, and lower albedo than other land uses. However, the long-term preservation of these services within protected areas depends on interventions in surrounding regions, particularly in the Amazon. Protecting and restoring these natural ecosystems is key for safeguarding ecosystem services and climate regulation in tropical regions.

Why does a decrease in cloud amount increase terrestrial evapotranspiration in a monsoon transition zone?

Terrestrial evapotranspiration plays a critical role in drought monitoring and water resource management. Changes in evapotranspiration are significantly influenced by cloud-related precipitation and radiation effects. However, the impact of cloud amount (CA) on evapotranspiration through its influence on precipitation remains uncertain, especially in the transition zone affected by the East Asian summer monsoon (EASM), which limits the understanding of the water cycle. Therefore, this study deeply explores the impact of CA on evapotranspiration and its potential physical mechanisms in Northwest China. The results show that the correlation between 31-year average evapotranspiration and CA is negative only in the semi-arid region and is positive in other climatic regions of Northwest China. This unique negative correlation is related to the change of precipitation pattern in the semi-arid region caused by the weak EASM. Smaller CA in weak monsoons results in more short-wave radiation reaching the surface, larger sensible heat, and weaker convective inhibition. Consequently, the proportion of convective clouds (CCs) increases and precipitation from these CCs enhances evapotranspiration. Less CA increases evapotranspiration and potentially exacerbates aridity in the semi-arid region of Northwest China. These results emphasize the role of cloud type in evapotranspiration. It is well known that global warming can change cloud type with more CCs. Therefore, this study sheds new light on evapotranspiration change under global warming.

Метеорологические условия и их сезонное распределение в ущелье Гушары бассейна реки Варзоб (Таджикистан)

The results of monitoring meteorological conditions in the middle part of the Varzob river basin in the Gushary gorge are presented. It is shown that for the period 1946–2021, atmospheric precipitation remains almost constant and the average annual temperature is characterized by an increasing trend. The seasonal distribution of temperature and atmospheric precipitation in the Gushary gorge of the Varzob river basin is characterized by the fact that the maximum precipitation corresponds to the spring season with maximum temperature in the summer season. It has been established that the average long-term temperature in the summer season in the Gushary gorge does not exceed 25°C that is due to the protection of the gorge from the penetration of air masses by high mountain ranges. A study and comparison of evapotranspiration in the gorge for 1950 and 2021 showed that for the period of more than seventy years there have been no significant changes in evapotranspiration.

Hydroclimatic Trends and Streamflow Response to Recent Climate Change: An Application of Discrete Wavelet Transform and Hydrological Modeling in the Passaic River Basin, New Jersey, USA

The exigency of the current climate crisis demands a more comprehensive approach to addressing location-specific climate impacts. In the Passaic River Basin (PRB), two bodies of research—hydroclimatic trend detection and hydrological modeling—have been conducted with the aim of revealing the basin’s hydroclimate patterns as well as the hydrologic response to recent climate change. In a rather novel application of the wavelet transform tool, we sidelined the frequently used Mann–Kendal (MK) trend test, to identify the hidden monotonic trends in the inherently noisy hydroclimatic data. By this approach, the use of MK trend test directly on the raw data, whose results are almost always ambiguous and statistically insignificant in respect of precipitation data, for instance, no longer poses a challenge to the reliability of trend results. Our results showed that, whereas trends in temperature and precipitation are increasing in the PRB, streamflow trends are decreasing. Based on results from the hydrological modeling, streamflow is more sensitive to actual evapotranspiration (ET) than it is to precipitation. In periods spanning decades with sufficient water availability, energy governs actual evapotranspiration rates, rendering streamflow more sensitive to increases in precipitation. Conversely, during meteorologically stressed decades, water availability dictates actual evapotranspiration, consequently amplifying streamflow sensitivity to fluctuations in actual evapotranspiration. We found that the choice of baseline condition constitutes an important source of uncertainty in the sensitivities of streamflow to precipitation and evapotranspiration changes and should routinely be considered in any climate impact assessment.

Evaluating the Climate Change Trends and Spatiotemporal Variations of Evapotranspiration: A Case Study in El-Beheira Governorate, Egypt

Aims: Evapotranspiration (ET) is crucial for determining crop water requirements, while climate change and global warming are major concerns. Therefore, in this study, we aimed at evaluating the climate change trends and the spatiotemporal variations in ET in a selected area located in El-Beheira Governorate, Egypt, while accounting for potential land use/land cover (LULC) changes. Methodology: We analyzed three Landsat images acquired in 1984, 2001, and 2020 to assess LULC changes in the study area. Climate change was studied from 1984 to 2021 using data from NASA's Prediction of Worldwide Energy Resource (POWER) project. We also used the Terra MODIS MOD16A3GF Version 6.1 ET product from 2000 to 2021 to evaluate the spatiotemporal variations of ET. Results: LULC change detection showed that the unchanged agricultural area from 1984 to 2020 accounted for 29.3% of the study area and was used to evaluate the changes of ET. Evaluating climate change revealed that there was an increased trend in temperature, relative humidity (RH), and precipitation, while no change was observed in wind speed. Similarly, the anomalies changes of temperature, RH, and precipitation had an increasing trend while wind speed was constant. On the other hand, the yearly ET values calculated from 2000 to 2021 had an increasing trend. There was a moderate correlation between RH and precipitation, as well as between ET and precipitation. Conclusion: The increased trends in climatic parameters such as temperature will eventually require changes in crop patterns to adjust to these changes and maintain a profitable yield. Furthermore, the increase in ET will result in an increase in crop water requirements, which is problematic, especially considering the limited water resources in Egypt.

The seasonal variability of future evapotranspiration over China during the 21st century

The evapotranspiration (ET) plays a crucial role in shaping regional climate patterns and serves as a vital indicator of ecosystem function. However, there remains a limited understanding of the seasonal variability of future ET over China and its correlation with environmental drivers. This study evaluated the skills of 27 models from the Six Phase of Coupled Model Intercomparison Project in modeling ET and the Bayesian Model Averaging (BMA) method was employed to merge monthly simulated ET based on the top five best-performing models. The seasonal changes in ET under three climate scenarios from 2030 to 2099 were analyzed based on the BMA-merged ET, which was well validated with observed ET collected from fourteen flux sites across China. Significant increasing ET over China are projected under all seasons during 2030–2099, with 0.05–0.13 mm yr−1, 0.11–0.23 mm yr−1, and 0.20–0.41 mm yr−1 under SSP1–2.6, SSP2–4.5 and SSP5–8.5 scenarios, respectively. Relative to the historical period (1980–2014), the relative increase in ET over China is highest in winter and lowest in summer. Seasonal ET increases significantly in all seven climate sub-regions under high forcing scenario. Higher ET increase is generally found in southeastern humid regions, while lowest ET increase occurs in northwest China. At the country level, the primary factor driving ET increase during spring, summer, and autumn seasons is the increasing net radiation and warming. In contrast, ET increase during winter is influenced not only by energy factors but also by vegetation-related factors. Future seasonal ET increase is predominantly driven by increasing energy factors in the southeastern humid region and Tibetan Plateau, while seasonal ET changes in the northwest region prevailingly depend on soil moisture. Results indicate that China will experience a “wet season will get wetter, and dry season will become drier” in the 21st century with high radiation forcing scenario.

Comparison of carbon and water fluxes and the drivers of ecosystem water use efficiency in a temperate rainforest and a peatland in southern South America

Abstract. The variability and drivers of carbon and water fluxes and their relationship to ecosystem water use efficiency (WUE) in natural ecosystems of southern South America are still poorly understood. For 8 years (2015–2022), we measured carbon dioxide net ecosystem exchange (NEE) and evapotranspiration (ET) using eddy covariance towers in a temperate rainforest and a peatland in southern Chile. NEE was partitioned into gross primary productivity (GPP) and ecosystem respiration (Reco), while ET was partitioned into evaporation (E) and transpiration (T) and used to estimate different expressions of ecosystem WUE. We then used the correlation between detrended time series and structural equation modelling to identify the main environmental drivers of WUE, GPP, ET, E and T. The results showed that the forest was a consistent carbon sink (−486 ± 23 g C m−2 yr−1), while the peatland was, on average, a small source (33 ± 21 g C m−2 yr−1). WUE is low in both ecosystems and likely explained by the high annual precipitation in this region (∼ 2100 mm). Only expressions of WUE that included atmospheric water demand showed seasonal variation. Variations in WUE were related more to changes in ET than to changes in GPP, while T remained relatively stable, accounting for around 47 % of ET for most of the study period. For both ecosystems, E increased with higher global radiation and higher surface conductance and when the water table was closer to the surface. Higher values for E were also found with increased wind speeds in the forest and higher air temperatures in the peatland. The absence of a close relationship between ET and GPP is likely related to the dominance of plant species that either do not have stomata (i.e. mosses in the peatland or epiphytes in the forest) or have poor stomatal control (i.e. anisohydric tree species in the forest). The observed increase in potential ET in the last 2 decades and the projected drought in this region suggests that WUE could increase in these ecosystems, particularly in the forest, where stomatal control may be more significant.

A past and present perspective on the European summer vapor pressure deficit

Abstract. The response of evapotranspiration to anthropogenic warming is of critical importance for the water and carbon cycle. Contradictory conclusions about evapotranspiration changes are caused primarily by their brevity in time and sparsity in space, as well as the strong influence of internal variability. Here, we present the first gridded reconstruction of the summer (June, July, and August) vapor pressure deficit (VPD) for the past 4 centuries at the European level. This gridded reconstruction is based on 26 European tree ring oxygen isotope records and is obtained using a random forest approach. According to validation scores obtained with the Nash–Sutcliffe model efficiency, our reconstruction is robust over large parts of Europe since 1600, in particular for the westernmost and northernmost regions, where most tree ring records are located. Based on our reconstruction, we show that from the mid-1700s a trend towards higher summer VPD occurred in central Europe and the Mediterranean region that is related to a simultaneous increase in temperature and decrease in precipitation. This increasing summer VPD trend continues throughout the observational period and in recent times. Moreover, our summer VPD reconstruction helps to visualize the local and regional impacts of the current climate change, as well as to minimize statistical uncertainties of historical VPD variability. This paper provides also new insights into the relationship between summer VPD and large-scale atmospheric circulation, and we show that summer VPD has two preferred modes of variability, namely a NW–SE dipole-like mode and a N–S dipole-like mode. Furthermore, the interdisciplinary use of the data should be emphasized, as summer VPD is a crucial parameter for many climatological feedback processes in the Earth's surface system. The reconstructed summer VPD gridded data over the last 400 years are available at the following link: https://doi.org/10.5281/zenodo.5958836 (Balting et al., 2022).

Changed evapotranspiration and its components induced by greening vegetation in the Three Rivers Source of the Tibetan Plateau

The Three Rivers Source (TRS), that is, the source of the Yangtze (SYZ), Yellow (SYE), and Lancang (SLC) Rivers in the Tibetan Plateau, is the water tower of Asia. Harsh climates, complex topography, and limited ground-based observations hinder our understanding of hydrological processes in this region, especially in a changing climate. Over the past two decades, the vegetation in the TRS has undergone significant greening as a result of the implementation of ecological restoration projections, which in turn has changed the hydrological process in this region. However, the impact of vegetation greening on evapotranspiration (ET) and its components is still unclear. Here, we investigate the response of ET and its components to vegetation changes in the TRS based on the maximum entropy production (MEP) model and detrending attribution analysis. The results show that the MEP model can well capture changes in ET at both the site and watershed scales. The multi-year-average ET of the TRS is 411.7 mm/a, of which the relative contributions of soil evaporation (Es), vegetation transpiration (Et), and canopy interception evaporation (Ei) are 68.21 %, 23.57 %, and 8.21 %, respectively. The annual ET has increased significantly, with a trend of 0.23 mm/a2 (p < 0.05). The contributions of vegetation greening to ET and its three components (Es, Et, and Ei) are 1.95 mm/a, −2.41 mm/a, 1.33 mm/a, and 3.03 mm/a, respectively. The findings are expected to provide guidance for the management of water resources and the implementation of ecological restoration in the TRS.

A doubled increasing trend of evapotranspiration on the Tibetan Plateau

Estimation of evapotranspiration (ETa) change on the Tibetan Plateau (TP) is essential to address the water requirement of billions of people surrounding the TP. Existing studies have shown that ETa estimations on the TP have a very large uncertainty. In this article, we discuss how to more accurately quantify ETa amount and explain its change on the TP. ETa change on the TP can be quantified and explained based on an ensemble mean product from climate model simulations, reanalysis, as well as ground-based and satellite observations. ETa on the TP experienced a significant increasing trend of around (8.4 ± 2.2) mm (10 a)−1 (mean ± one standard deviation) during 1982–2018, approximately twice the rate of the global land ETa (4.3 ± 2.1 mm (10 a)−1). Numerical attribution analysis revealed that a 53.8% TP area with the increased ETa was caused by increased temperature and 23.1% part was due to soil moisture rising, because of the warming, melting cryosphere, and increased precipitation. The projected future increase in ETa is expected to cause a continued acceleration of the water cycle until 2100.

Assessing spatiotemporal characteristics of atmospheric water cycle processes over the Tibetan Plateau using the WRF model and finer box model

The Tibetan Plateau (TP) is the highest and one of the most extensive plateaus in the world and serves as a hotspot of climate change. In the context of climate warming, changes in evapotranspiration (ET) and external water vapor transport have a significant impact on assessing atmospheric water cycle processes over the TP. By using the Weather Research and Forecasting (WRF) model for long-term simulations and the finer box model for the calculation of water vapor along the boundary of the TP, the external atmospheric water vapor transport and its spatiotemporal characteristics over the TP are finely described. The simulated precipitation and ET are well-simulated compared with observation. Research results show that: (1) The total water path on the TP decreases from southeast to northwest. Water vapor is mainly transported into the TP from the western and southern boundaries. The net water vapor flux transported from the western boundary to the TP by westerly wind is negative, while the net water vapor flux transported from the southern boundary to the TP by southerly wind is positive. (2) In spring and winter, water vapor is mainly transported into the TP by mid-latitude westerlies from the western boundary. In summer, water vapor transport controlled by mid-latitude westerlies weakens, and water vapor is mainly transported into the TP from the southern boundary. In autumn, water vapor controlled by mid-latitude westerlies gradually strengthens, and water vapor is mainly transported into the TP from the western boundary. In addition, the ratio of ET to precipitation on the TP is about 0.48, and the moisture recycling is about 0.37. Water vapor mainly comes from external water vapor transport.

High-resolution land surface modeling of the irrigation effects on evapotranspiration over the Yellow River basin

Accurate estimation of irrigation-induced evapotranspiration (ET) is critical for understanding the terrestrial water cycle. However, current estimation has large uncertainties due to the model limitations and the lack of accurate water use data. In this study, a water-energy balanced irrigation scheme is incorporated into the Conjunctive Surface-Subsurface Process version 2 (CSSPv2) model to improve the hydrological simulations over the Yellow River basin (YRB) where irrigation is extensive. The coupled model (CSSPv2-IRR) is calibrated against long-term water use data from provincial survey, and it is used to perform a 6-km resolution simulation over the YRB during 1991–2017. The results show that the coupled model can well reproduce hydrological processes within the basin, and the simulated irrigation amount, ET and surface soil moisture largely agree with the validation datasets. Specifically, the annual irrigation amount and irrigation-induced ET changes from the CSSPv2-IRR are more reasonable than ISIMIP2a and reanalysis products, with a reduction in bias by 79.5–97.3 % and 81.2–98.8 % respectively. The CSSPv2-IRR model simulation suggests that irrigation-induced annual ET change is 26.4 mm/year during 1991–2017, contributing to an 8.9 % increase in annual ET over the YRB, and the increase can reach 44.3 % over major irrigation districts. In addition, the contribution of irrigation to long-term increasing trend in ET over the irrigation districts in the upper reach is greater than the contribution of climate change. This study suggests a growing control of irrigation on the ET over the YRB, which has implications for regional water cycle and water resources management.

Improvement of evapotranspiration simulation study in the Hailar River basin under the influence of vegetation dynamics

In arid and semi-arid areas with <400 mm of precipitation, evapotranspiration (ET) accounts for about 80% of precipitation and is the main water consumer in the watershed. However, vegetation greening in recent years will increase ET and exacerbate the aridity of the area by affecting soil moisture in the root system. Vegetation changes are regional and spatially heterogeneous, therefore, in order to characterize ET changes under vegetation dynamics, it is necessary to expand the spatial scale of ET simulation. However, widely used evapotranspiration simulation models, such as the Shuttleworth-Wallace model (SW model), are deficient in reflecting the direct and indirect effects of vertical (i.e., soil depths) and horizontal (i.e., vegetation dynamics) directions. Based on field sampling and constructed structural equation model (SEM), we found that vegetation dynamics affect evapotranspiration not only directly, but also indirectly by affecting soil moisture at different depths. On this basis, we defined the weighting coefficients of 0.85 and 0.15 for grassland vegetation zones, 0.3, 0.15, 0.20, 0.25, 0.10 for forest-grass interspersed zones, and 0.20, 0.55, 0.25 for forested zones, respectively, based on the SEM results. Different soil moisture weighting coefficients were defined within different vegetation type zones and the improved SW model is called S-W-α. Comparing the simulation results with the measured data, S-W-α improved the ET simulation accuracy in this region by 33.92% and the improved ET spatial trend can respond to the dynamic changes of vegetation. Replacing the ET module in the Block-wise use of TOPMODEL and Muskingum-Cunge method mode (BTOP model) with the modified S-W-α, the results show that the simulation accuracy of the improved model is increased by 25%, and the Nash is higher than 75% for both the rate period and the validation period, which realizes the extension of the model from the point scale to the basin scale. The modified model may provide technical support for simulation of evapotranspiration and management of ecosystem health in ecologically fragile areas.