Decrease In Evapotranspiration Research Articles

Evidence of field‐scale shifts in transpiration dynamics following bark beetle infestation: Stomatal conductance responses

AbstractAmplified eruptive outbreaks of bark beetles as a consequence of climate change can cause tree mortality that significantly affects terrestrial water and carbon fluxes. However, the lack of field‐scale observations of underlying physiological mechanisms currently hampers the expression of such ecosystem disturbances in predictive modelling. Based on a unique flux tower dataset from a subalpine forest located in the Rocky Mountains, mechanisms of stomatal response to an extensive bark beetle outbreak were investigated using various models and parametrizations. The datasets cover a decade, including the periods of pre‐infestation, infestation, and post‐infestation. Field measurements showed considerable decreases in evapotranspiration (ET), transpiration (T), and leaf area index (LAI) during the two‐year infestation period compared to the pre‐infestation period. Model interpretations of observed water and carbon fluxes indicated that the overall reductions in T were not solely due to decreased LAI, but also to changes in physiological behaviours. The summer season's canopy‐scale stomatal conductance was significantly reduced during the infestation period, from 0.0018 to 0.0011 m s−1. One primary reason for the observed variations is likely that the bark beetle infestation hampers the water transport in the xylem. The damage of xylem has important implications for water use efficiency (WUE), which also significantly influences the parameterization of stomatal conductance. When using stomatal conductance models to forecast ecosystem dynamics, it is crucial to recalibrate the model's parameters to ensure the accurate depiction of stomatal dynamics during various infestation periods. The neglect of the temporal variability of canopy‐scale stomatal conductance under ecosystem disturbances (e.g., bark beetle infestations) in current earth system models, therefore, requires specific attention in assessments of large‐scale water and carbon balances.

Assessment of the effects of climate change on water balance components in the upper Erer subbasin, Ethiopia

Eastern Ethiopia watersheds are located in transition zone from Arid to semi-humid climate and in expanding to westwards the west annual rainfall is highly declining. This paper explains future hydrological response impacts under changing climate using ensemble average of the CORDEX RCMs for historical (1979–2014) and future (2024–2070) periods. The result revels the monthly average temperature varies (0.04–6.25°C) for RCP-4.5, while it varies (0.03–6.59°oC) for RCP-8.5. The monthly average rainfall to be decline by 90.71 mm and rise by 211. 22 mm for RCP-4.5, while it is going to decline by 84.97 mm and rise by 235.62 mm for RCP-8.5. The adjusted SWAT model was used to detect the changes of projected hydrological response from reference period. Balance components of the baseline period was compared to future period. The result shows the change in decrease of annual mean surface flow (4.98 %–5.63 %), groundwater flow (5.63 %–6.68 %), evapotranspiration (2.45 %–2.57 %) and water yield (5.54 %–5.21 %) to be expected from RCP-4.5 to RCP-8.5. The findings of this paper provide valuable assistance to water resource planners by enhancing their comprehension of change in climate effects at local level.

Revisiting the hydrological legacy of revegetation on China's Loess Plateau using Eagleson's ecohydrological perspective

Revegetation has resulted in a trend of increasing vegetation greenness on the Chinese Loess Plateau. However, it remains unclear whether the regional vegetation coverage exceeds hydroclimatic limitations in the context of revegetation, and the hydrological effects of greening are controversial. Eagleson's optimality hypothesis can explain some of the hydrological effects on the Loess Plateau. Here, building on previous research, the geospatial vegetation states were estimated for pre- and post-revegetation periods on the Loess Plateau from 1982 to 2015 using Eagleson's ecological optimality theory. Additionally, a drought composite analysis approach was utilized to investigate the hydrological effects related to drought (including sensitivity and partitioning) under various vegetation states. It was found that revegetation increased the proportion of catchments in the equilibrium state and decreased the proportion in the disturbed state, owing to a wetter climate compared with the pre-revegetation period. Root-zone soil drought, driven by precipitation (P) deficit, asymmetrically triggered hydrological effects for both the pre- and post-revegetation periods, with reduced runoff (Q) for both periods and a decrease in evapotranspiration (ET) during the pre-revegetation period but an increase in ET during the post-revegetation period. Moreover, catchments in an equilibrium state exhibited lower sensitivity between ET and P, and more stable partitioning of ET with regards to P, compared with those in a disturbed state. These results underscore the theoretical framework that an equilibrium state is crucial for maintaining ecosystem ET. Our results highlight the necessity of considering the hydrologic regulation of vegetation states when assessing the hydrological effects of vegetation change.

Constraints on hopanes and brGDGTs as pH proxies in peat

pH is one of the major parameters governing peat functioning, and pH variations in modern peatlands affect carbon and methane production and consumption. Paleo-pH reconstructions have been limited thus far, but they could help to better understand peat functioning in variety of settings and also serve as an indirect proxy for climatic and environmental variations such as precipitation. Bacterial hopanes and branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) were investigated in a 10-ka peat record from North-East Cameroon (NGaoundaba, Western Central Africa). Recently developed pH proxies using the hopane ββ/(αβ + ββ) ratio and the brGDGT cyclization ratio (CBTpeat) were applied and compared with previously published bulk organic data from the same core. Different hypotheses are usually proposed to explain the high abundance of the “thermally mature” C31 αβ hopane in peats: acid-catalyzed isomerization of ββ to αβ isomers with or without biological mediation or the direct input of C31 αβ hopanes by bacteria. In the NGaoundaba peat deposit, the opposite variation in the ββ/(αβ + ββ) ratio of C30 and C31 hopanes and the carbon isotopic composition of C31 ββ and αβ hopanes suggest that an eventual transformation of C31 ββ to αβ isomers is not possible without biological mediation. A linear correlation between hopane- and brGDGT-reconstructed pH is observed, suggesting a similar response to environmental changes for these two independent proxies. A large increase in reconstructed pH values coincides with changes in vegetation and precipitation at the end of the African Humid Period (AHP). Lower pH values are observed during the AHP, coinciding with a period of increased precipitation and consistent with bulk organic data and slightly higher C31 ββ hopane δ13C values compared to middle and late Holocene. Bulk organic data indicate an interruption of the AHP by a drier intermission that coincides with a decrease in reconstructed pH values, probably reflecting a decrease in evapotranspiration. Variations in pH values could be interpreted in terms of preservation of peat organic matter and might reflect past changes in methane cycling in the investigated peatland. The present study reinforces the idea that reconstruction of pH in peat deposits represents a promising proxy of environmental change, enabling a better understanding of changes in peat functioning over large timescales and various locations.

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.

Future water storage changes over the Mediterranean, Middle East, and North Africa in response to global warming and stratospheric aerosol intervention

Abstract. Water storage plays a profound role in the lives of people across the Middle East and North Africa (MENA) as it is the most water-stressed region worldwide. The lands around the Caspian and Mediterranean seas are simulated to be very sensitive to future climate warming. Available water capacity depends on hydroclimate variables such as temperature and precipitation that will depend on socioeconomic pathways and changes in climate. This work explores changes in both the mean and extreme terrestrial water storage (TWS) under an unmitigated greenhouse gas (GHG) scenario (SSP5-8.5) and stratospheric aerosol intervention (SAI) designed to offset GHG-induced warming above 1.5 ∘C and compares both with historical period simulations. Both mean TWS and extreme TWS are projected to significantly decrease under SSP5-8.5 over the domain, except for the Arabian Peninsula, particularly in the wetter lands around the Caspian and Mediterranean seas. Relative to global warming, SAI partially ameliorates the decreased mean TWS in the wet regions, while it has no significant effect on the increased TWS in drier lands. In the entire domain studied, the mean TWS is larger under SAI than pure GHG forcing, mainly due to the significant cooling and, in turn, a substantial decrease in evapotranspiration under SAI relative to SSP5-8.5. Changes in extreme water storage excursions under global warming are reduced by SAI. Extreme TWS under both future climate scenarios is larger than throughout the historical period across Iran, Iraq, and the Arabian Peninsula, but the response of the more continental eastern North Africa hyper-arid climate is different from the neighboring dry lands. In the latter case, we note a reduction in the mean TWS trend under both GHG and SAI scenarios, with extreme TWS values also showing a decline compared to historical conditions.

Effects of land use/land cover change on hydrological responses of a watershed in the Central Rift Valley of Ethiopia

Abstract The purpose of this study is to evaluate the impacts of LULC changes on the hydrological components of a watershed using multivariate statistics, and hydrological modeling approaches. The study analyzed the LULC distributions, and changes corresponding to the years 2000, 2010, and 2020. The SWAT model was then applied to assess the hydrological impacts of these changes in the studied watershed. Finally, changes in LULC types were correlated with the water balance components using a Partial Least Squares Regression (PLSR) method. The result showed a continuous expansion of barren, built-up, and cropland areas, while forests, shrubs, and grassland decreased by about 67.12, 41, and 36.88%, respectively. The modeling result showed that surface runoff, water yield, and evapotranspiration decreased by 16.1, 2.9, and 9.3%, respectively. In contrast, base flow, soil water storage, and lateral flow of the watershed increased by up to 19.1%, 55.9%, and 150.4%, respectively, due to LULC changes. The PLSR model identified the cropland, forest, and shrub LULC types as the major factors affecting the water resource components. The study results provide useful information for policymakers and planners in the implementation of sustainable water resource planning and management in the context of environmental change.

Influence of human-induced land use change on hydrological processes in semi-humid and semi-arid region: A case in the Fenhe River Basin

Study Region: The Fenhe River Basin (FRB) is an important tributary of the Yellow River Basin and locate in a semi-arid and semi-humid region in northwest China. Over the past four decades, significant anthropogenic activities have resulted in significant land use and land cover change (LUCC) that have markedly impacted hydrological processes in FRB.Study Focus: To analyze land use changes under multiple historical land use scenarios from LU1980 to LU2015, and to establish the Water and Energy transfer Processes in Large basins (WEP-L) model to quantify the influences of LUCC on hydrological processes, particularly on baseflow.New hydrological insights for the region: LUCC from LU1980 to LU2015 resulted in a 14.5 % increase in water yield (WY) and a 2.7 % and 1.4 % decrease in baseflow (BF) and evapotranspiration, respectively. Urbanization led to a significant increase in WY and a reduction in BF, exhibiting strong spatial gradients between urban centers and their peripheries. Increases in forestland decreased WY, while ET showed no significant change due to large absolute values and moisture limitations. Furthermore, the response of BF to forest cover exhibits spatial variation. A negative correlation between BF and forest cover was evident in upstream, whereas no significant correlation was observed in downstream. The findings of this study offer valuable insights for land use planning and sustainable watershed management in semi-arid semi-humid region.

Spatiotemporal changes and driving factors of reference evapotranspiration and crop evapotranspiration for cotton production in China from 1960 to 2019

Introduction: Understanding and tracking changes in crop water requirements is crucial for effective irrigation, water planning, and future decisions. Determining the reference evapotranspiration (ETO) and crop evapotranspiration (ETC) of China cotton is essential for water resource management.Methods: This study analyzed the spatiotemporal changes in ETO and ETC at 248 standard stations in cotton production regions of China from 1960 to 2019, and the ETO and ETC of each station were quantified by using the CropWat 8.0 and non-parametric Mann-Kendall test. The impacts of climate change on ETO and ETC were evaluated by analyzing the contribution rate and sensitivity coefficient of climate change.Discussion: The results revealed distinct distributions of ETO and ETC across various growth stages and spatial scales in the cotton production regions of China. In the Huanghe Valley, the rate of decline for ETO decreased from 787.23 mm to 769.84 mm, while in the Yangtze Valley cotton region, it decreased from 749.19 mm to 735.01 mm. Similarly, in the Northwest inland cotton regions, the rate of decline for ETO reduced from 991.19 mm to 982.70 mm. As for ETC, the rate of decline decreased from 677.62 mm to 654.33 mm in the Huanghe Valley, from 653.02 mm to 625.50 mm in the Yangtze Valley, and from 916.25 mm to 886.74 mm in the Northwest inland cotton regions. ETO was highly sensitive to maximum air temperature (Tmax), followed by relative humidity (RH), sunshine duration (SD), wind speed at 2 m height (WS), and minimum air temperature (Tmin). WS was the most influential climate variable associated with ETO change, followed by Tmax, SD, RH, and Tmin. Significant declines in WS and SD were indicated in the decrease in ETO in the Huanghe Valley and Yangtze Valley cotton regions. WS showed a significant decrease in ETO in the northwestern inland cotton region. However, decreased RH and increased temperature commonly reversed the trend of ETO from 2000 to 2019, and the northwestern inland cotton region had the most significant upward trend. Amidst high temperatures and drought stress, the irrigation needs of cotton were rising, posing a significant threat to both cotton production and water resources.

Contribution rates of climate variables to the change in reference evapotranspiration in northern Thailand from 1991 to 2019

AbstractHigher temperatures are expected to increase evaporation and reference evapotranspiration (ETo). However, a decrease in ETo has been observed in numerous regions worldwide. ETo is controlled by climate variables besides temperature; wind speed, air humidity, and radiation, which vary according to regional climatic conditions, may also be drivers. Few studies have quantified the sensitivity and contributions of climate variables to ETo change in tropical savanna climates. Long‐term (1991–2019) climate time series in northern Thailand was used to assess the trends in ETo and determine which climate variables exert the strongest control on ETo, during the rainy and non‐rainy season, as an example for the tropical savanna climate. Furthermore, this study used the proportion of contribution and sum of positive (negative) contribution and classified the results into five groups to analyse the change in ETo. This helped to determine the climate variable with the highest contribution. From this study, ETo was the most sensitive to the maximum temperature, followed by sunshine duration in both rainy and non‐rainy seasons. Furthermore, the variables that contributed the most to the long‐term change in ETo were sunshine duration and wind speed. The increase (decrease) in sunshine duration and wind speed contributed to the increase (decrease) in ETo in this area. Understanding ETo changes and determining whether ETo has a strong tendency to change are the basis for water resource planning and management in the region.

Surface‐driven amplification of Madden–Julian oscillation circulation anomalies across East Africa and its influence on the Turkana jet

AbstractIn semi‐arid environments, rainfall‐driven soil moisture fluctuations exert a strong influence on surface turbulent fluxes. Intraseasonal rainfall variability can therefore impact low‐level atmospheric temperatures and influence regional circulations. Using satellite observations and an atmospheric reanalysis, we investigate whether rainfall variability induced by the Madden–Julian oscillation (MJO) triggers land–atmosphere feedbacks across East Africa.We identify that surface fluxes during the East African wet seasons (March–May and October–December) are sensitive to MJO‐induced precipitation variations across low‐lying regions of South Sudan and highland regions of Uganda and southwest Kenya. For example, during MJO phases 6 to 8, when rainfall is suppressed, surface temperatures and sensible heat fluxes increase, whilst evapotranspiration decreases. Spatial variations in the surface flux response to rainfall variability feed back onto the atmosphere through amplifying MJO‐associated pressure anomalies. During dry MJO events for instance, surface warming across the exit region of the Turkana channel increases the low‐tropospheric along‐channel pressure gradient and intensifies the Turkana jet. We conclude that average surface‐driven temperature fluctuations during a single day are responsible for approximately 12% of MJO‐associated variability of the Turkana jet speed. However, we expect that the accumulation of heat over multiple days to the west of the East African Highlands further amplifies anomalies in the pressure gradient and jet intensity. Modelling experiments are required to quantify the accumulated impact of the surface forcing. Surface‐driven Turkana jet variations influence the East African moisture budget and affect the intensity and inland propagation of coastal convection. Not only is this the first study to investigate the importance of intraseasonal land–atmosphere feedbacks across East Africa, but it is also the first to show that Turkana jet characteristics are partly driven by surface conditions. This work motivates an investigation into whether subseasonal forecast models fully harness the predictability from surface‐induced jet variations.

Estimating ecosystem evaporation and transpiration using a soil moisture coupled two-source energy balance model across FLUXNET sites

The two-source energy balance model coupled with soil moisture (TSEB-SM) was evaluated against observations from a global set of 57 eddy covariance (EC) sites, part of the FLUXNET2015 dataset. In addition, modeled soil evaporation (E) and transpiration (T) were compared with the values obtained from the Transpiration Estimation Algorithm (TEA) and underlying water use efficiency (uWUE) approaches. The TSEB-SM model framework using near-surface soil moisture improved the agreement to EC-observed sensible and latent heat fluxes, reducing mean absolute percentage error (MAPE) by about 30% and root mean square error (RMSE) by about 44 W/m2 across all sites. The results show that the advantage of the TSEB-SM model, with respect to the original TSEB, becomes more evident as the ratio of actual to potential evapotranspiration (AET/PET) decreases. The E and T produced by TSEB-SM has better correlation with the results of uWUE partitioning than TSEB, especially under low soil water content condition. Likewise, TSEB-SM is superior to TSEB in simulating T when compared with sap flow measurements derived from the SAPFLUXNET database. These results imply that the development and application of TSEB-SM has made significant advances in modeling surface water fluxes, even though uncertainties remain. The approach used in TSEB-SM, driving the model with an extensive remotely sensed parameter set, gives valuable information on water use and provides an alternative to Global Climate Models where complex interactions of ecosystems are parametrized. Thus, TSEB-SM provides a unique insight into the flow of energy and the role of surface fluxes in the global water cycle.

Estimation and Spatiotemporal Evolution Analysis of Actual Evapotranspiration in Turpan and Hami Cities Based on Multi-Source Data

The accurate inversion of actual evapotranspiration (ETa) at a regional scale is crucial for understanding water circulation, climate change, and drought monitoring. In this study, we produced a 1 km monthly ETa dataset for Turpan and Hami, two typical arid cities in northwest China, using multi-source remote sensing data, reanalysis information, and the ETMonitor model from 1980 to 2021. We analyzed the spatiotemporal variation of ETa using various statistical approaches and discussed the impact of climate and land use and cover changes (LUCC) on ETa. The results show the following: (1) the estimation results correlate well with ETa products on monthly scales (coefficient of determination (R2) > 0.85, root mean square error (RMSE) < 15 mm/month) with high reliability. (2) The ETa values were spatially distributed similarly to precipitation and LUCC, with the multi-year (1980–2021) average of 66.31 mm and a slightly fluctuating downward trend (−0.19 mm/a). (3) During the 42-year period, 63.16% of the study area exhibited an insignificant decrease in ETa, while 86.85% experienced pronounced fluctuations (coefficient of variation (CV) > 0.20), and 78.83% will show an upward trend in the future. (4) ETa was significantly positively correlated with precipitation (94.17%) and insignificantly positively correlated with temperature (55.81%). The impact of human activities showed an insignificant decreasing trend (85.41%). Additionally, the intensity of ETa varied considerably among land types, with the largest for cropland (424.12 mm/a). The results of the study have implications for promoting the rational allocation of regional water resources and improving water use efficiency in arid zones.

Different hydrological controls causing variable rates of Holocene peat growth in a lowland valley system, north-eastern Netherlands; implications for valley peatland restoration

The Drentsche Aa valley system in the glacial sandy landscape of the north-eastern Netherlands, is one of the many regional drainage systems in the north-western to central European Lowlands. Following deep incision in the Weichselian, ca 7 m of eutrophic peat has accumulated in the lower to middle reaches of the valley system in the Holocene, completely filling the Weichselian incision. We reconstructed the rate of water-level rise controlling peat growth at three locations in the valley system (representing the upper, middle and lower reaches), using 14C peat dates from compaction-free sampling sites on the sloping valley margin where the peat directly overlies the sandy Pleistocene subsurface. The 14C dates enabled the construction of curves showing the water-level evolution at each location. Our results show variable rates of Holocene peat growth in the valley system in response to different drivers of hydrological change: a strong increase in annual precipitation (onset Holocene), a decrease in evapotranspiration (10,000–8000 cal. years BP) and relative sea-level rise (after ~4500 cal. years BP). Because the identified hydrological controls on peat growth are regional, they probably ruled Holocene peat growth in many peat-filled valley systems in the north-western to central European Lowlands. Currently, there is growing attention for these valley systems in the context of European nature restoration efforts and climate change adaptation and mitigation measures. The present study underscores that large-scale hydrological measures outside the valley system are needed for restoration of degraded valley peatlands.

Impacts of Ongoing Land-Use Change on Watershed Hydrology and Crop Production Using an Improved SWAT Model

The southern Ogallala Aquifer continues to deplete due to decades of irrigation with minimal recharge. Recently enacted regulations limiting groundwater withdrawals and the potential for farm profitability with cotton production systems indicate driving forces for increased cotton production acreage in the Northern High Plains of Texas (NHPT). This study focused on evaluating the land-use change from corn or winter wheat to cotton under irrigation and dryland conditions in the Palo Duro watershed (PDW) in the NHPT using an improved Soil and Water Assessment Tool (SWAT) model. Land-use change from irrigated corn to irrigated cotton led to reductions in average (2000–2014) annual irrigation, actual evapotranspiration (ETa), and surface runoff by 21%, 7%, and 63%, respectively. Nevertheless, the replacement of irrigated wheat with irrigated cotton caused irrigation and ETa to increase by 46% and 18%, respectively. Land-use conversion from dryland wheat to dryland cotton showed 0.1% and 15% decreases in ETa and surface runoff, respectively. More than 40% reductions in simulated cotton yields were found when the cotton planting area was moving northward to the cooler NHPT. The ongoing change in land use provided an option to lengthen the water availability of the southern Ogallala Aquifer for irrigation.

Faster evapotranspiration recovery compared to canopy development post clearcutting in a floodplain forest

Actual evapotranspiration (ETa) is a key component of the water balance, and its accurate quantification of spatiotemporal variation is essential to improve the understanding of soil–plant-atmosphere-hydrosphere interactions. While in situ point measurements allow for the determination of the ETa of a particular ecosystem or land cover type, remote sensing methods make it possible to divide and evaluate the rate of ETa of different ecosystems in the landscape and would allow better management of the water resource system, especially if those are partly or permanently limited. The goal of this paper was to analyze the impact of clearcutting during standard forest management practices in floodplain forests and its effect on the water regime of the area. We selected the Lanžhot floodplain forest area (48.681°N 16.950°E, 155 m a.s.l.) that represents a biologically and hydrologically unique area of remnant floodplain forest within the upper Danube River basin. Since clearcutting represents a drastic intervention into the ecosystem including changes in canopy structure and local microclimate, we hypothesized that the impact of the clearcut on the overall water balance is long-term in the order of decades as a result consequence of logging of the mature forest and changes in local microclimatic conditions in disturbed areas. To analyze the impacts of clearcutting on ETa, we applied the METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) remote sensing model. METRIC was validated in the Central European climatic conditions using two ground eddy covariance measurements systems over grassland and floodplain forest. The evaluated model METRIC was then applied to quantify ETa in three areas of interest in the floodplain forest, where in 2015–2021, mature vegetation was targeted for removal, modification of the soil surface, and subsequent planting of a new generation of English oak trees (Quercus robur L.). Immediately after the removal of vegetation cover, METRIC detected an annual decrease in ETa by 35–40%, while leaf area index (LAI) decreased by 70–80%. This was followed by a quick recovery of the ETa/ETo (where ETo represents FAO-56 reference evapotranspiration), reaching similar values as uncut surrounding vegetation during the third year, while LAI recovery was detected in the fifth year after the removal of vegetation cover. The rapid recovery of the ETa/ETo rejected the initial hypothesis, and studies showed that the newly formed stand replaced the ETa/ETo rate of the mature stand in the floodplain forest conditions of Central Europe in the fourth year, suggesting that the impacts of clearcutting on the hydrology may be temporally relatively limited.

Changes In Land Use/ Cover And Water Balance Components During 1964–2010 Period In The Mono River Basin, Togo-Benin

The Intergovernmental Panel on Climate Change has predicted that sub-tropical regions are more vulnerable to climate change’s negative effects (CC). Additionally, to CC, land use and land cover (LULC) changes and dam construction, often neglected, play an important role in the spatial and temporal distribution of water balance components (WBC) for agricultural production and socio-ecological equilibrium. This study aimed to analyze and compare the changes in LULC and WBC for the period before Nangbéto dam construction (1964–1986) and the period after its construction (1988–2010) in the Mono River Basin (MRB). To this end, the study used mainly WBC extracted from the validated Soil and Water Assessment Tool and LULC data of 1975–2000 in the MRB to explore their temporal distributions and the link in their changes. The results showed that mean actual monthly evapotranspiration, percolation, water yield, surface runoff, groundwater, and lateral flow represent 51%, 17.5%, 15.9%, 9.4%; 5.7% and 0.4%, respectively, of total water balance between 1964 and 1986. The same components represented 51%, 9.1%, 20.4%, 6.3%, 10.6% and 2.6%, respectively, between 1988 and 2010. The contribution of these WBC in the mean-annual (1964–1986) period was for actual evapotranspiration (31.3%), water yield (25.9%), percolation (17.7%), groundwater (14.71%), surface runoff (9.94%) and lateral flow (0.40%). Meanwhile, between 1988 and 2010, the contribution of actual evapotranspiration, water yield, percolation, groundwater, surface runoff and lateral flow is 49.8%,19.9%, 11.2%, 10.3%, 6.1%, and 2.5%, respectively. The results showed that the peaks of the actual evapotranspiration, surface runoff, percolation and water yield appeared in September, corresponding to a month after the maximum rainfall in August. However, our more detailed analysis showed that a significant decrease in forest and savanna and an increase in croplands led to a decrease in actual evapotranspiration and lateral flow over the second simulation period compared to the first period of simulation over the MRB scale. These findings showed that sustainable management and conservation of natural vegetation are crucial for integrated water resource management and conservation in MRB.

Wildfire Burn Severity Affects Postfire Shifts in Evapotranspiration in Subalpine Forests

Highlights After wildfire, actual evapotranspiration (ETa) in four subalpine areas decreased proportionally to burn severity. High-severity burn areas maintained the highest ETa before fire and the lowest ETa after fire. After fire, ETa decreased more in areas that had higher prefire ETa. ETa was a useful system-level measure of susceptibility to fire and impact after fire. Abstract. The ecohydrologic response to fire is complex, with devastating consequences for source-water hydrology. Postfire canopy structure, leaf area, infiltration, and soil-water storage all may act to reduce evapotranspiration (ET), a key hydrologic variable and indicator of ecohydrologic function. This study explored the use of 30-m resolution Landsat-based SSEBop-model estimates of actual ET (ETa) to assess the effects of fire in the Upper Rio Grande Basin (2002 Million Fire, CO; 1996 Hondo Fire, NM; 2002 Montoya Fire, NM; 2000 Cerro Grande Fire, NM). SSEBop ETa data from 1985-2019 were analyzed to better understand postfire response and recovery in several sub-alpine burned areas. Results show step reductions in ETa after fire across all burn severities in all four fire areas. Prior to the fire, ETa was generally higher in high-severity burn areas, indicative of higher fuel loads, although high variability indicated the influence of additional factors. All areas had a greater response (decreased ETa) to fire in high-severity areas and a lesser response as burn severity decreased. The decrease in ETa after high-severity fire ranged from 42% to 63%, compared to the decrease after low-severity fire, which ranged from 24% to 44%. None of the four burn areas demonstrated postfire ETa recovery after 17 to 23 years. This study demonstrates the clear utility for remote-sensing ETa estimates as a system-level measure of susceptibility to fire, impact of fire, and, potentially, recovery after fire. However, additional research is needed to account for the covariate effects of other fuel, topographic, weather, and climate factors. Keywords: Ecohydrology, Postfire recovery, Remote sensing, Upper Rio Grande Basin.

Drip irrigation improves spring wheat water productivity by reducing leaf area while increasing yield

To mitigate the climate change-induced water shortage and realize the sustainable development of agriculture, drip irrigation, a more efficient water-saving irrigation method, has been intensively implemented in most arid agricultural regions in the world. However, compared to traditional border irrigation, how drip irrigation affects the biophysical conditions in the cropland and how crops physiologically respond to changes in biophysical conditions in terms of water, heat and carbon exchange remain largely unknown. In view of the above situation, to reveal the mechanism of drip irrigation in improving spring wheat water productivity, paired field experiments based on drip irrigation and border irrigation were conducted to extensively monitor water and heat fluxes at a typical spring wheat field (Triticum aestivum L.) in Northwest China during 2017–2020. The results showed that drip irrigation improved yield by 10.3 % and crop water productivity (i.e., yield-to-evapotranspiration-ratio) by 15.6 %, but reduced LAI by 16.9 % in contrast with border irrigation. Under drip irrigation, the lateral development of spring wheat roots was promoted by higher soil temperature combined with frequent dry-wet alternation in the shallow soil layer (0–20 cm), which was the basis for efficient absorption of water and fertilizer, as well as efficient formation of photosynthate. Meanwhile, drip irrigation increased net radiation and decreased latent heat flux by inhibiting leaf growth, thereby increased sensible heat, causing a higher soil temperature (+1.10 ℃) and canopy temperature (+1.11 ℃). Further analysis proved that soil temperature was the key factor affecting yield formation. Based on the above conditions, the decrease in leaf distribution coefficient (−0.030) led to the decrease in evapotranspiration (−5.7 %) and the increase in ear distribution coefficient (+0.029). Therefore, drip irrigation emphasized the role of soil moisture in the soil-plant-atmosphere continuum, enhanced crop activity by increasing field temperature, especially soil temperature, and finally improved yield and water productivity via carbon reallocation. The study revealed the mechanism of drip irrigation for improving spring wheat yield, and would contribute to improving Earth system models in representing agricultural cropland ecosystems with drip irrigation and predicting the subsequent biophysical and biogeochemical feedbacks to climate change.

Sensitivity of evapotranspiration and seepage to elevated atmospheric [formula omitted] from lysimeter experiments in a montane grassland

The response of vegetation to elevated atmospheric carbon dioxide (eCO2) has opposing effects on terrestrial water fluxes, especially evapotranspiration. In particular, CO2 fertilization may enhance plant growth, therefore increasing canopy transpiration, while a partial stomatal closure decreases leaf transpiration. In this study, the effects of eCO2 on water fluxes at a managed montane grassland were monitored using two high precision weighable lysimeters exposed to ambient and elevated (+300 ppm relative to ambient conditions) CO2 concentrations. During the growing season, eCO2 led to a general decrease in evapotranspiration and an increase in seepage. It was shown that eCO2 influences evapotranspiration primarily through the change in stomatal resistance, as no effect of eCO2 on the leaf area index was confirmed. A CO2-dependent Penman–Monteith equation and actual evapotranspiration data from the lysimeters made it possible to estimate the effect of eCO2 on stomatal resistance. eCO2 was found to increase stomatal resistance by 50% relative to ambient conditions. A HYDRUS-1D model allowed a temporal extension of the experimental findings to the period of 1990–2021 and revealed high variability in the relative change in annual seepage under eCO2. The modeling exercise demonstrated that the effect of eCO2 can be easily implemented in the Penman–Monteith equation, and if neglected, leads to overestimation of transpiration and underestimation of seepage, especially in the first post-drought seepage events. Our findings show that eCO2 positively affects the water balance in montane grasslands, thus eCO2 might be an important factor in mitigating the effects of warming and droughts in the future. We propose that the vegetation response to eCO2, in particular the effect on stomatal resistance, should be taken into account when assessing the effects of climate change on grassland water fluxes. This may also have large implications when studying the impact of climate change at a watershed scale.