Response Of Evapotranspiration Research Articles

Spatiotemporal variations and driving factors of evapotranspiration in the Yunnan-Guizhou Plateau from 2003 to 2020

ABSTRACT Evapotranspiration (ET) is vital for the Earth's energy and water balance, particularly influenced by global climate change. The Yunnan-Guizhou Plateau (YGP), characterized by abundant water resources and intricate terrain, has been a subject of study. However, previous research often overlooked intra-annual climate variations in ET. This study employed high-spatiotemporal resolution ET data from 2003 to 2020 to quantitatively analyze the spatiotemporal characteristics of ET on the YGP. The annual ET showed an increasing trend of 0.18 mm/year, with monthly ET increases in January, March, November, and December, mainly influenced by vegetation transpiration, which accounts for 56% of ET. Breakpoints in ET trends and seasonal components occurred in January 2007 and June 2018. The geodetector model assessed the impact of 15 driving factors on ET, with net radiation and vegetation index playing dominant roles with q-values of 0.29 and 0.24. Factor impacts varied seasonally, with greater influence in the dry season (q-value of 0.53 for net radiation in January) and lesser in the rainy season (q-value of 0.08 in August). Pearson correlation analysis indicated that different driving factors influenced ET in different months. These findings enhance understanding of plateau ET responses to climate change mechanisms.

Released control of vapor pressure deficit on rainfed rice evapotranspiration responses to extreme droughts in the subtropical zone

Released control of vapor pressure deficit on rainfed rice evapotranspiration responses to extreme droughts in the subtropical zone

Globally assessing how evapotranspiration feedbacks govern the impacts of multi-year droughts

Multi-year droughts constitute a natural experiment for testing the hydrological legacy across different climate regimes. Evapotranspiration (ET) responses to drought have not been fully elucidated because the underlying mechanisms involve complex interactions of climate, soil, and vegetation. This study collected monthly hydrometeorological data during 1982–2011 from 1069 catchments worldwide to investigate multi-year droughts and their impacts on ET and to analyse the underlying mechanisms of ET. As expected, multi-year droughts generally induced ET reductions across different climate regimes, while ET exhibited asymmetric hydrological responses with a greater portion of precipitation (P) being partitioned into ET in water-limited regions, and a smaller portion of P being partitioned in ET in energy-limited regions. Multi-year droughts induced soil moisture droughts and leaf area index decreases, which often led to increases in the vapour pressure deficit, while inconsistent responses occurred for air temperature. Interestingly, when long-term catchment wetness [i.e., (precipitation − streamflow) / precipitation] exceeded 0.50 we found that catchment wetness played a vital role in controlling the response of catchment properties to climate changes. During the multi-year droughts, attribution analysis revealed the enhanced role of available water (represented by P) in controlling ET, followed by available energy and vegetation. Although vegetation played vital role in controlling ET in energy-limited regions, it was P that controlled ET during drought periods. Taken together, these findings indicate that ET responses and their underlying mechanisms induced by multi-year droughts vary under different climate regimes. Specifically, a two-stage mechanism drove the ET responses in wet catchments, suggesting that catchments with higher catchment wetness (>0.50) could more effectively mitigate the impact of multi-year droughts.

Enhanced decreases in rice evapotranspiration in response to elevated atmospheric carbon dioxide under warmer environments.

A short period of exposure to elevated CO2 is known to decrease evapotranspiration via stomatal closure. Based on theoretical evaluation of a canopy transpiration model, we hypothesized that this decrease in the evapotranspiration of rice under elevated CO2 was greater under higher temperature conditions due to an increased sensitivity of transpiration to changes in CO2 induced by the greater vapour pressure deficit. In a temperature gradient chamber-based experiment, a 200 ppm increase in CO2 concentration led to 0.4 mm (-7%) and 1.5 mm (-15%) decreases in 12 h evapotranspiration under ambient temperature and high temperature (+3.7°C) conditions, respectively. Model simulations revealed that the greater vapour pressure deficit under higher temperature conditions explained the variations in the reduction of evapotranspiration observed under elevated CO2 levels between the temperature treatments. Our study suggests the utility of a simple modelling framework for mechanistic understanding of evapotranspiration and crop energy balance system under changing environmental conditions.

Development and evaluation of the interactive Model for Air Pollution and Land Ecosystems (iMAPLE) version 1.0

Abstract. Land ecosystems are important sources and sinks of atmospheric components. In turn, air pollutants affect the exchange rates of carbon and water fluxes between ecosystems and the atmosphere. However, these biogeochemical processes are usually not well presented in Earth system models, limiting the explorations of interactions between land ecosystems and air pollutants from regional to global scales. Here, we develop and validate the interactive Model for Air Pollution and Land Ecosystems (iMAPLE) by upgrading the Yale Interactive Terrestrial Biosphere Model with process-based water cycles, fire emissions, wetland methane (CH4) emissions, and trait-based ozone (O3) damage. Within iMAPLE, soil moisture and temperature are dynamically calculated based on the water and energy balance in soil layers. Fire emissions are dependent on dryness, lightning, population, and fuel load. Wetland CH4 is produced but consumed through oxidation, ebullition, diffusion, and plant-mediated transport. The trait-based scheme unifies O3 sensitivity of different plant functional types (PFTs) with the leaf mass per area. Validations show correlation coefficients (R) of 0.59–0.86 for gross primary productivity (GPP) and 0.57–0.84 for evapotranspiration (ET) across the six PFTs at 201 flux tower sites and yield an average R of 0.68 for CH4 emissions at 44 sites. Simulated soil moisture and temperature match reanalysis data with high R above 0.86 and low normalized mean biases (NMBs) within 7 %, leading to reasonable simulations of global GPP (R=0.92, NMB=1.3 %) and ET (R=0.93, NMB=-10.4 %) against satellite-based observations for 2001–2013. The model predicts an annual global area burned of 507.1 Mha, close to the observations of 475.4 Mha with a spatial R of 0.66 for 1997–2016. The wetland CH4 emissions are estimated to be 153.45 Tg [CH4] yr−1 during 2000–2014, close to the multi-model mean of 148 Tg [CH4] yr−1. The model also shows reasonable responses of GPP and ET to the changes in diffuse radiation and yields mean O3 damage of 2.9 % to global GPP. iMAPLE provides an advanced tool for studying the interactions between land ecosystems and air pollutants.

Estimating Evapotranspiration in the Qilian Mountains Using GRACE/GRACE-FO Satellite Data

Evapotranspiration (ET) is the most significant constituent of the response to climate warming. It serves as a crucial link in the soil–vegetation–atmospheric continuum. Analyzing the driving forces and response of ET to regional-scale climate warming holds scientific significance in improving global water resource assessment methods and drought monitoring techniques. The innovation presented in this article is the calculation of ET by using GRACE/GRACE-FO satellite data through the water balance equation. The inter-annual and seasonal changes in ET in different regions of the Qilian Mountains were analyzed, along with quantifying the contribution of environmental meteorological factors to ET. The ETGRACE and ETMonitor products have good consistency, with a monthly correlation coefficient of 0.92, an NSE coefficient of 0.80, and a root mean square error of 10.38 mm. The results indicate that the increasing trend of ET in the Qilian Mountains region exhibits a “medium–high–low” distribution pattern. The rate of increase in ET is 5.2 mm/year in the central segment. In spring and summer, the overall trend of ET is an increasing one. However, the central and western segments exhibit a slight decreasing trend of ET in autumn. During winter, the southern part of the Qilian Mountains experiences a notable reduction in ET. The correlation between the changes in ET and soil moisture exhibited a strong association, with soil moisture change contributing significantly to ET: 57.8% for the eastern section, 52.8% for the middle section, and 46.9% for the western section. The thermal effect primarily controls ET variations within eastern sections, where temperature change accounts for approximately 6.7% of the total variation in ET levels. Conversely, the moisture factor dominates western sections, where precipitation change accounts for about 6.5% of the total variation in ET levels. Due to the distinct gradient characteristics of environmental meteorological factors in the central segment, the fluctuation of these factors collaboratively drives ET changes. This article provides a new approach for obtaining continuous and reliable actual evapotranspiration in high-altitude areas.

Response of evapotranspiration to the 2022 unprecedented extreme drought in the Yangtze River Basin

AbstractThe response of evapotranspiration (ET) to drought is essential for understanding water availability under drought conditions, which has received increasing scientific attention but remains highly uncertain. An unprecedented extreme drought sweeping the whole Yangtze River Basin during the summer and autumn of 2022 provides a novel opportunity to explore the ET response to drought within large river basins. Here, we apply multiple ET products to investigate the spatiotemporal variation of ET during the 2022 extreme drought and analyse the response of ET to drought in the Yangtze River Basin. The results show that this drought, characterized by widespread substantial precipitation deficit and high level of atmospheric evaporative demand (AED), leads to evident abnormal ET. Over the whole basin, ET exhibits a notable increase in the initial 2 months of this drought, which can significantly reduce water availability. However, despite continued high AED, the increase in ET fails to remain in the following months due to limited moisture supply. This suggests that ET response to drought varies as drought progresses. Among other drought events from 2003 to 2022, the response of ET is similar to that in the 2022 extreme drought. Specifically, for most sub‐basins, ET typically shows positive anomalies in the early stage of drought, followed by negative anomalies in the late stage. Generally, our findings improve the understanding of the dynamic response of ET to drought at the basin scale, which is crucial for basin water security.

Vegetation and Evapotranspiration Responses to Increased Atmospheric Vapor Pressure Deficit across the Global Forest

A forest is vulnerable to drought and plays important roles in the regulation of carbon and water cycling in a terrestrial ecosystem. Atmospheric vapor pressure deficit (VPD) has been identified as an increasingly major factor in plant functioning and has been established as a main contributor to recent drought-induced plant mortality, independent of other drivers associated with climate change. However, most previous studies have focused on the effects of climate warming and CO2 enrichment on vegetation growth, without considering the effects of an increased VPD on vegetation growth and evapotranspiration (ET) in forest ecosystems. This could lead to a large uncertainty in estimating the variability in forest carbon sinks. Based on the long-term satellite data, we investigated the response of the leaf area index (LAI) and ET to the VPD via a partial correlation analysis in this study. We also examined the temporal variability in the partial coefficients within a ten-year moving window. The results showed that over 50% of the region displayed a negative partial correlation between the LAI, ET, and VPD, and those pixels were mainly concentrated in North America and the plains of Eastern Europe. Regions with a negative trend of partial correlation in both the LAI and ET are mostly located in the plains of Eastern Europe and the Siberian Plain of western Russia, while the positive trend is mainly in South America. The plains of Eastern Europe are becoming drier, which was proved by the interannual trend of the Standardized Precipitation Evapotranspiration Index (SPEI) and soil water content (SWC). Additionally, the LAI and ET in those areas exhibited a significant positive correlation with the SWC based on the moving window average. This study suggests that the role of the VPD on vegetation will become increasingly prominent in the context of future climate change for the forest ecosystem.

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).

Environmental Controls on Evapotranspiration and Its Components in a Qinghai Spruce Forest in the Qilian Mountains.

Qinghai spruce forests, found in the Qilian mountains, are a typical type of water conservation forest and play an important role in regulating the regional water balance and quantifying the changes and controlling factors for evapotranspiration (ET) and its components, namely, transpiration (T), evaporation (Es) and canopy interceptions (Ei), of the Qinghai spruce, which may provide rich information for improving water resource management. In this study, we partitioned ET based on the assumption that total ET equals the sum of T, Es and Ei, and then we analyzed the environmental controls on ET, T and Es. The results show that, during the main growing seasons of the Qinghai spruce (from May to September) in the Qilian mountains, the total ET values were 353.7 and 325.1 mm in 2019 and 2020, respectively. The monthly dynamics in the daily variations in T/ET and Es/ET showed that T/ET increased until July and gradually decreased afterwards, while Es/ET showed opposite trends and was mainly controlled by the amount of precipitation. Among all the ET components, T always occupied the largest part, while the contribution of Es to ET was minimal. Meanwhile, Ei must be considered when partitioning ET, as it accounts for a certain percentage (greater than one-third) of the total ET values. Combining Pearson's correlation analysis and the boosted regression trees method, we concluded that net radiation (Rn), soil temperature (Ts) and soil water content (SWC) were the main controlling factors for ET. T was mainly determined by the radiation and soil hydrothermic factors (Rn, photosynthetic active radiation (PAR) and TS30), while Es was mostly controlled by the vapor pressure deficit (VPD), atmospheric precipitation (Pa), throughfall (Pt) and air temperature (Ta). Our study may provide further theoretical support to improve our understanding of the responses of ET and its components to surrounding environments.

Divergent Responses of Summer Terrestrial Evapotranspiration to Cloud Increase in East Asia

AbstractCloud impact on terrestrial evapotranspiration (ET) can be significant, while a fundamental understanding of ET response to cloud change has not been addressed in regional aspects. In this study, seven ET datasets from satellite and land surface models are used to analyze the summer ET in response to low cloud cover (LCC) over East Asia, in combination with satellite microwave and optical vegetation data, as well as ERA5 climatic and surface parameters. In general, all ET datasets present a strong negative relationship with LCC over dense vegetation (e.g., forests), which leads to the ET reduction of more than −0.5 mmday−1 under the large LCC increase, compared with the least cloudy sky conditions. Such reduction is stronger under more humid and denser forests (aridity index AI > 0.5 and enhanced vegetation index EVI > 0.6). In contrast, a positive relationship between ET and LCC presents over arid and sparse lands (AI < 0.2 and EVI < 0.2), accompanied by enhanced ET (>0.2 mmday−1). Analysis shows that under increased LCC conditions, substantial reduction in radiation availability results in the decline in both plant transpiration (ETveg) and soil evaporation (ETsoil) over humid dense vegetation, dominating the overall negative response. The increase of near‐surface relative humidity over arid sparse vegetation may indicate a stronger moisture availability, which promotes ETsoil and partly offsets the negative effect of radiation reduction. The change of vegetation water content, indicated by a satellite microwave vegetation index, is important for ETveg over arid mountainous lands with cloud cover. These findings contribute new insights to the understanding of vegetation‐atmosphere interactions.

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.

Anthropogenic Influences Alter the Response and Seasonality of Evapotranspiration: A Case Study Over Two High Mountain Asia Basins

AbstractEarth's vegetation has been increasing over the past decades, altering water and energy cycles by changing evapotranspiration (ET). Greening, caused by climatic and anthropogenic factors, has high rates in High Mountain Asia (HMA). Here we focus on two HMA basins (the Yangtze and the Ganges‐Brahmaputra) to contrast the impacts of climate‐ and human‐induced greening on ET. Though the rate of greening is similar in both basins, anthropogenic influences lead to dissimilar responses in ET. In the Yangtze, climate‐induced greening increases ET, with the increase in moisture being high enough to meet the ET demand. In the Ganges‐Brahmaputra, irrigation‐induced greening does not alter annual ET, only pre‐monsoon ET increases. The dry season declines in water storage due to pumping decrease ET, while laboriously meeting the demand. This study provides a representative example of the contrasting influences of climate induced and anthropogenic driven processes on the seasonality of ET.

Weakened Increase in Global Near‐Surface Water Vapor Pressure During the Last 20 Years

AbstractIt is well known that global warming increases the atmospheric water vapor content, which results in substantial changes in the hydrological cycle. Using five observational data sets, the results show that an increasing trend of near‐surface water vapor pressure (AVP) over land and ocean was significant from 1975 to 1998, while such an increasing trend in AVP subsequently weakened from 1999 to 2019. This phenomenon is associated with decreased oceanic evaporation and land surface evapotranspiration in response to recent climate variations. One consequence of such a phenomenon is a large increase in near‐surface vapor pressure deficit (VPD), which in turn increases atmospheric demand for water vapor and thus aridity and drought over land. This result emphasizes the importance of water vapor change under global warming.

Response of Evapotranspiration, Photosynthetic Characteristics and Yield of Soybeans to Groundwater Depth

To clarify the physiological mechanism of different groundwater depths affecting soybean evapotranspiration, photosynthetic characteristics and yield, a field experiment with four groundwater depth levels (1 m (D1), 2 m (D2), 3 m (D3) and 4 m (D4)) was conducted through the groundwater simulation system in 2021 and 2022. In this study, a quantitative analysis was conducted on the groundwater recharge and irrigation water demand and evapotranspiration (ET) of soybean fields with different treatments, and the effects of different treatments on soybean leaf area index (LAI), chlorophyll content index (SPAD), intercepted photosynthetic active radiation (IPAR), photosynthetic gas exchange parameters, dry matter accumulation (DMA) and yield were explored. The results showed the following: (1) Groundwater depth affected soybean ET and the source of ET. With the increase in groundwater depth, groundwater recharge and its contribution to ET gradually decreased, but the amount of irrigation required gradually increased, resulting in the ET as D1 &gt; D4 &gt; D2 &gt; D3. (2) Soybean LAI, SPAD and IPAR were significantly affected by the different groundwater depths, of which the D1 treatment always maintained the maximum, followed by the D4 treatment, and the D3 treatment was the minimum. The photosynthetic gas exchange parameters under different treatments changed synergistically, showing significant differences in the flowering and podding stages, notably D1 &gt; D4 &gt; D2 &gt; D3. Soybean DMA and yield first decreased and then increased with the increase in groundwater depth, and the average DMA and yield under the D1 treatment increased by 27.71%, 46.80% and 22.82% and 20.29%, 29.91% and 12.83% in the two years, respectively, compared to the D2, D3 and D4 treatments. (3) The structural equation model demonstrated that the groundwater depth indirectly affected the growth of soybean leaf area by affecting groundwater recharge, which in turn regulated soybean ET and photosynthetic capacity and ultimately affected DMA and yield. The above results showed that in the case of shallow groundwater depth (D1), the largest groundwater recharge promoted the growth of soybean leaf area and chlorophyll synthesis and increased the absorption and utilization of solar radiation. And it improved the leaf stomata conditions, accelerated the gas exchange between the plant and atmosphere, enhanced the photosynthetic production capacity and ET and achieved maximum DMA and yield. Soybean leaf growth and photosynthesis diminish with the increase in groundwater depth. In the case of deep groundwater depth (D4), the maximum irrigation improved the growth and photosynthetic performance of soybean leaves, which was favorable to ET, and ultimately led to increases in DMA and yield.

Cascade effects of climate and vegetation influencing the spatial variation of evapotranspiration in China

Evapotranspiration (ET) is generally affected by climate and vegetation, but the main factor controlling the spatial variation of ET largely varied with different regions. Clarifying the characteristics and dominant factor of ET in China is essential for understanding the regional ecosystem water balance. This study quantitatively assessed the magnitude and spatial variations of ET in China's terrestrial ecosystems using data measured by eddy covariance from 150 observation sites and investigated its underlying direct and indirect influencing factors. The results demonstrated that the ET of China's terrestrial ecosystems varied from 146.95 to 1125.33 mm, with an average value of 551.00 ± 204.12 mm. The ET showed a general increasing trend from the North to South, aligning with the latitudinal patterns of water availability (mean annual precipitation (MAP)), energy conditions (mean annual net radiation (MARn), and mean annual temperature (MAT)). Compared to regions at the same latitude, the North China Plain exhibited relatively higher ET because of the extensive cropland sites in the area. Furthermore, significant positive linear correlations were found between ET and MAT in the majority of ecosystems. However, a negative correlation of ET with MAT was observed in grasslands, which may be attributed to inconsistent responses of ET to MAT on the Tibetan Plateau and Inner Mongolia. Fractional vegetation coverage (FVC) exhibited a more significant direct influence on ET than climate factors (MARn, MAT, and MAP). Nevertheless, climate factors not only exert a direct influence on ET but also have cascade effects that affect FVC, thereby indirectly influencing the ET. When considering these cascade effects, MAP emerged as the dominant driver of spatial variations in ET of China's terrestrial ecosystems. This study provides essential information on variations of ET in China's terrestrial ecosystem and valuable insights for future explorations into the adaptive mechanisms underlying spatial variations of ET.

Climate variability impact on crop evapotranspiration in the upper East region of Ghana

Ghana's agriculture is primarily rain-fed, making it vulnerable to the impact of climate variability and climate change. This study examined the trends and impact of climatic variability and evapotranspiration on the crop evapotranspiration of selected staple crops across three districts in the Upper East region of Ghana over a 19-year period. Data on agro-climatic conditions (rainfall, temperature, relative humidity, and sunlight) in the Upper East region were obtained from the Ghana Meteorological Agency (GMet) from 2000 to 2018. Given the non-conformity of the response variables to the normality assumption, the Quantile Regression (QR) was employed to examine the impact of climatic variability on different crop evapotranspiration scenarios (low = 10 %, typical = 50 %, and high = 90 %) of the selected crops. The analyzes disclosed a significant difference in crop evapotranspiration between the districts, except for maize, which remained consistent. There was an increase in crop evapotranspiration trend for all, but the maize crop informs the potential improvement of crop evapotranspiration notwithstanding the climatic variability. The study offers a vital insight into the complex dynamics of crop evapotranspiration in response to climatic variability and evapotranspiration. It is recommended, therefore, to consider advances in crop varieties through continuous investment in crop breeding research programmes to improve drought tolerance crops and develop regional water balance techniques.

Land use and land cover change impact on characteristics of surface evapotranspiration in semi-arid environment of Western Rajasthan, India

Abstract The development of the Indira Gandhi Nahar Pariyojana (IGNP) in western Rajasthan has significantly impacted land use and land cover (LULC) changes, which have hugely transformed the hydrologic cycle in recent decades. Hence, we investigate the surface evapotranspiration (ET) response to LULC changes in the IGNP for the period from 1990 to 2020. The Surface Energy Balance algorithm (Surface Energy Balance Algorithm for Land) was applied to the Landsat dataset along with local weather data obtained from the Indian Meteorological Department. A machine learning-based random forest classifier was applied to develop the LULC maps. The higher values of ET are mainly distributed in the northwest. Area covered by croplands has shown an increasing trend over the decades at a rate of 734.76 km2·a−1, urban settlements/ built-up areas increased at a rate of 14.67 km2·a−1, barren area decreased gradually at a rate of 751.67 km2·a−1, and area covered by the few water bodies showed minor fluctuations. Overall, the LULC changes have a smaller influence on ET rates but has a considerable impact on the total ET in the IGNP region due to an increase in the area covered by vegetation as a result of increased water availability.

Modeling land-atmosphere energy and water exchanges in the typical alpine grassland in Tibetan Plateau using Noah-MP

Study regionAlpine grassland in the Tibetan Plateau Study focusThis study used Noah-MP to simulate the energy fluxes [net radiation (Rn), latent (λE) and sensible (H) heat fluxes] in two typical alpine ecosystems in the Tibetan Plateau. The effectivenesses of new parameterization schemes for the roughness length for heat transfer and the root distribution were evaluated. By further using multi-scenario modeling, the responses of land evapotranspiration (ET), soil evaporation (Es) and vegetation transpiration (Tr) to changes in precipitation, solar radiation and air temperature were investigated. New hydrological insights for the regionThe default Noah-MP largely overestimates (underestimates) Rn and λE, but tends to underestimate (overestimate) H in alpine meadow (alpine steppe). After incorporating two newly-developed parameterization schemes, the accurancy of Noah-MP has been improved in alpine meadow for Rn and λE, while in alpine steppe only H has been improved. The ET, Es and Tr in alpine meadow are more sensitive to decreasing precipitation than that to increasing precipitation. In alpine steppe, ET and Es increase with increasing precipitation, while Tr responds weakly to changes in precipitation; The effect of temperature change on ET appears weak in both ecosystems. However, Tr shows negative responses to increased temperature and such responses in alpine steppe are more remarkable than those in alpine meadow, suggesting the former may be more vulnerable to future warming than the latter.

Altered landscape pattern dominates the declined urban evapotranspiration trend

Urbanization has significantly altered the regional hydrological cycle and thermal environment. However, the response of urban evapotranspiration (ETu) to these altered urban landscape patterns remains unclear. This study proposes a hybrid ETu model that combines physics processes and machine learning to evaluate trends and drivers of ETu across 480 cities in China. The results indicate that the long-term average ETu across the 480 cities is 508 mm, and the average rate of decline in ETu (DRETu) across the 480 cities is 2.19 mm/year. DRETu exhibits a positive correlation with the increasing rate of urban aridity index (AI) and fractional impermeable surface coverage (fi). The decrease in ETu is primarily caused by the altered urban landscape patterns, which include: 1) reductions in urban vegetation and water body areas resulting from urbanization; and 2) the substitution of natural forest land with landscape grasslands in urban areas. We further investigated the correlation between the urban heat island (UHI) effect and ETu and found that the intensified UHI effect is caused by an increased difference in ETu between the main urban area and the suburbs. The results of this study emphasize the significance of constructing water bodies and green infrastructure in the central urban area, as well as restoring natural forests, to enhance the thermal comfort of the urban environment.