Increase In Potential Evapotranspiration Research Articles

Climate Change Scenarios for Impact Assessment: Lower Zab River Basin (Iraq and Iran)

Selecting appropriate climate change scenarios is crucial, as it influences the outcomes of climate change impact studies. Several storylines could be used to investigate the sensitivity of water resource schemes to weather variability and improve policymakers’ adaptation strategies. This study proposes a comprehensive and generic methodology for assessing the future climate change impact on semi-arid and arid zones at the basin scale by comparing delta perturbation scenarios to the outcomes of seven collections of GCMs (general circulation models). The findings indicate that the two scenarios predicted nearly identical declines in average reservoir discharges over a monthly timescale. Consequently, their maximum values are almost similar. The projected decrease in the streamflow for the period 2080–2099 is approximately 48%—the same as the ratio from the delta perturbation scenario of Future16 (a 30% precipitation decrease and a 30% potential evapotranspiration increase). Furthermore, delta perturbation scenarios allow the impacts of model sensitivity to climate change to be clearly identified in relation to GCM scenarios. Delta perturbation scenarios allow for an extensive collection of possible climate changes at the regional scale. In addition, delta perturbation scenarios are simpler to create and use; therefore, they might complement GCM scenarios.

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.

Analysis of change process of NPP dominated by human activities in Northwest Hubei, China, from 2000 to 2020.

Clarifying the spatial distribution of the impact of different human disturbance activities on the net primary productivity (NPP) in regions with single climatic conditions is of considerable importance to ecological protection. Time-series NPP from 2000 to 2020 was simulated in Northwest Hubei, China, and the effects of the climate and human activities on the NPP changes were separated. Research results showed that from 2000 to 2020, the NPP change with an area of 10,166.63 km2 in Northwest Hubei is influenced by climate and human activities. Among them, human activities account for as high as 84.53%. From 2000 to 2020, the NPP in Northwest Hubei showed a slight upward trend at a rate of 1.61g C m-2year-1. The significantly increased NPP accounted for 21.4% of the total, which was mainly distributed in north of Northwest Hubei. And the farming of cultivated land led to the increase of NPP in west as well as the reduced human distribution in cultivated land, which was scattered in forests. Only 6.67% of the total area demonstrated a significantly decreased NPP, which was distributed mainly in the central affected by the expansion of rural-urban land and change of broad-leaved forests to shrubs and in southeast regions of Northwest Hubei caused by the increase in potential evapotranspiration. This study refined the driving factors of spatial heterogeneity of NPP changes in Northwest Hubei, which is conducive to rational planning of terrestrial ecosystem protection measures.

Understanding climate change impacts on drought in China over the 21st century: a multi-model assessment from CMIP6

The future state of drought in China under climate change remains uncertain. This study investigates drought events, focusing on the region of China, using simulations from five global climate models (GCMs) under three Shared Socioeconomic Pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5) participating in the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3b). The daily Standardized Precipitation Evapotranspiration Index (SPEI) is employed to analyze drought severity, duration, and frequency over three future periods. Evaluation of the GCMs’ simulations against observational data indicates their effectiveness in capturing historical climatic change across China. The rapid increase in CO2 concentration under high-emission scenarios in the mid- and late-future century (2040–2070 and 2071–2100) substantially influences vegetation behavior via regulation on leaf stomata and canopy structure. This regulation decelerates the increase in potential evapotranspiration, thereby mitigating the sharp rise in future drought occurrences in China. These findings offer valuable insights for policymakers and stakeholders to develop strategies and measures for mitigating and adapting to future drought conditions in China.

Calibration of the DSSAT-CERES Wheat Crop Model under Scenarios of Climate Change Adaptation and Biotic Stress

A field experiment was conducted during the 2018/2019 wheat growing season in Kafr El-Sheikh Governorate. This is to assess the potential impact of climate change on wheat production under different irrigation treatments using the DSSAT-CERES wheat simulation model and climate change scenarios; to determine the best sowing date to be used as an adaptation strategy under climate change scenarios. The model effectively simulates wheat yield, with a high goodness of fit and d-Stat value, and low root mean square per observation, resulting in an overall goodness of fit of average 13.8 kg/fed. The model's performance was satisfactory, with high R2 and d-Stat values and low RMSE/obs, with overall values of 0.830, 0.951, and 2.3 mm, respectively for water consumption. The CERES-Wheat model accurately simulates wheat yield and water consumption, allowing us to assess climate change's impact on wheat yield in 2030 and 2040. The study shows a decrease in solar radiation (SR) by 1.9 and 2.1 MJ/m2/day in 2030 and 2040, while maximum temperature increases by 1.5 and 1.9°C due to climate change, and minimum temperature decreases by 1.8 and 2.3°C in 2030 and 2040. This results in an increase in potential evapotranspiration (PET) by 0.2 and 0.3 mm. The study predicts that season length will shorten in 2030 and 2040 due to temperature increases. In 2030, it will be reduced by 2, 4, and 4 days under different treatments. In 2040, it will be lower, with reductions of 3, 5, and 5 days. The study found that wheat yield losses would be lowest under the first sowing date and irrigation treatment, while the highest reductions were found under the third treatment. Climate change will reduce wheat water consumption due to shorter growing seasons and heat stress, with the lowest reductions occurring in 2030 and 2040 at 8 and 18%, respectively. The highest reductions in wheat yield were observed under the third sowing date and irrigation treatment. We suggest planting wheat in November, using full irrigation to prevent high-yield losses, and implementing adaptation strategies to reduce wheat plant vulnerability to climate change risks.

Climate change impacts on spatial and seasonal meteorological drought characteristics for the island of Ireland

AbstractUnderstanding how climate change is likely to impact on meteorological droughts is key to informing adaptation planning. For Ireland, little research has examined how droughts are likely to change in future. Here we examine changes in the monthly climate water balance, aridity index and changes in magnitude, frequency and duration of droughts using standardized drought indices for the island of Ireland derived from bias‐adjusted CORDEX simulations for the 2080s (2070–2099), forced with a high (RCP8.5) and moderate (RCP4.5) emissions pathway. Findings highlight that increases in potential evapotranspiration, driven by increasing temperature, together with changing seasonal rainfall patterns increase aridity in summer with water deficits extending into spring months, especially in the east and midlands by the end of the century. Increases in drought frequency and magnitude are also evident, with greatest increases for RCP8.5. Critically, increases are considerably greater for the standardized precipitation evapotranspiration index (SPEI) than for the standardized precipitation index (SPI), emphasizing the importance of using metrics that capture potential evapotranspiration in monitoring and assessing future drought risk. Summer and spring show the greatest increase in drought magnitude and frequency, most marked in the east of the island. By contrast, multiseasonal droughts, assessed using 6‐month accumulation periods show more modest changes in magnitude and duration. The resultant impacts of climate change on drought for Ireland would require considerable adaptation given the vulnerabilities exposed by the 2018 drought.

Quantification and allocation of uncertainties of climate change impacts on hydropower potential under 1.5 °C and 2.0 °C global warming levels in the headwaters of the Benue River Basin, Cameroon

Hydropower is the world's largest producer of renewable energy and represents more than 43% of the low-carbon energy. However, it is sensitive to climate variability and change. This study evaluates the climate change impacts on hydropower potential in the headwaters of the Benue River Basin (HBRB) under 1.5 °C and 2.0 °C global warming levels (GWLs) and quantifies the main sources of uncertainty in the modeling chain. Precipitation and temperature from 17 members of the Coordinated Regional Downscaling Experiment over the Africa domain (CORDEX-Africa) under two representative concentration pathways (RCPs 4.5 and 8.5) were used to run two calibrated Lumped-conceptual hydrological models (HMs) (Hydrologiska Byrans Vattenavdelning (HBV-Light) and HYdrological MODel (HYMOD)). An analysis of variance (ANOVA) decomposition was used to quantify the uncertainties related to each impact modeling chain step in the hydropower potential calculation process. Results reveal a high uncertainty in both climatic and hydrologic parameters. The change in precipitation associated with an increase in potential evapotranspiration (PET) causes a significant decrease in hydropower generation associated with a large uncertainty range. The ANOVA sensitivity test reveals that the dominant contributing source to hydropower projections uncertainty varies with GWL. Given the likely breach of GWL 1.5 by the early 2030s, these findings contribute information for consideration in water and energy planning in the region over the next decade, and stresses that these considerations are urgent for the socioeconomic well-being of the region.

Impact of Climate Change and Consumptive Demands on the Performance of São Francisco River Reservoirs, Brazil

Climate change in the coming decades could intensify extreme events such as severe droughts. Combined with the possible increase of water demands, these changes exert a great deal of pressure on the water systems. In order to confirm this assumption, a set of scenarios was proposed in this study to consider the combined impact of climate changes and the increase in water demand on the main multiple-use reservoirs of São Francisco River, Brazil. For this purpose, five CMIP6 climate models were used, considering two greenhouse gas emissions scenarios: the SSP2-4.5 and SSP5-8.5. The affluent natural flows and regulated flows were estimated to the adopted reservoirs considering all existing, new and projected demands. The combination of scenarios indicated an increase in Potential Evapotranspiration; possible significant reduction in water availability, with a decrease in precipitation with a magnitude of −15% in the most pessimistic scenarios and a decrease in flows with a magnitude varying between −5% and −40% in the Sobradinho and Três Marias reservoirs; growth in water demand, mainly for irrigation, with annual rates of 6.80%, 7.42%, 10.99% and 9.29% for Itaparica, Sobradinho, Três Marias and Retiro Baixo, respectively; and a substantial reduction in the performance of the evaluated reservoirs, mainly for the Retiro Baixo and Itaparica reservoirs, which showed a high vulnerability index and a low sustainability index.

Future changes of dry‐wet climate regions and its contributing climatic factors in China based on CMIP6 models

AbstractUnderstanding future dry and wet changes under global climate change is of great regional significance in China. Based on six Global Climate Models (GCM) from the Coupled Model Intercomparison Project phase 6 (CMIP6), we project the changes of dry‐wet climate regions in China in the 21st century under the three SSP‐RCP (shared socioeconomic pathway‐representative concentration pathway) scenarios (SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5), and further identify the key climatic factors that lead to the transition of dry‐wet climate regions. The results show the area of humid and subhumid regions in China will show an upward trend in the future, while the area of semiarid and arid regions will show a downward trend. Especially under the SSP5‐8.5 scenario, the area of the subhumid region has the largest increase trend (0.042% per year), and the area of the arid region has the largest decline trend (−0.048% per year). The three main transfer directions of dry‐wet climate regions are from arid to semiarid regions, from semiarid to subhumid regions, and from subhumid to humid regions in the future. Due to the future extensive wetting trend in the north, the future dry‐wet climate regions will shift to wetter types in Tibet, North China, the Qinling‐Huaihe regions and the northeast. In addition, the key climatic factors for the transition of dry‐wet climate regions are mainly precipitation, maximum temperature and solar radiation. The increase of precipitation plays a dominant role for areas projected to change to wetter types, and the increase of potential evapotranspiration (PET) plays a dominant role for areas projected to change to drier types. The PET changes in changed areas of dry‐wet climate regions are mainly dominated by maximum temperature and solar radiation. Our research has important implications for future water resource management and reconsideration of climate mitigation and adaptation policies.

Trend and spatial-temporal variation of drought characteristics over equatorial East Africa during the last 120 years

Centennial drought characteristics in Equatorial East Africa (EEA) is investigated using the Standardized Precipitation Evapotranspiration Index (SPEI) derived from the Climatic Research Unit (CRU) dataset. The spatial pattern of drought distribution, as well as drought duration, intensity and frequency, are analyzed for SPEI at a 3-month timescale for March-April-May (MAM) season. Rotated Empirical Orthogonal Function (REOF), Mann-Kendall method (MK), and wavelet analyses are used to study drought’s spatial pattern, trend, and periodicity. The result of the principal component analysis returned six homogenous drought sub-regions. A low drought frequency characterizes EEA (<20%). The drought in the MAM season lasts between 2.2 and 2.8 months. Overall, the result showed a weak long-term drying trend for most parts of EEA that were significant in some sub-regions and insignificant in others. An increase in drought areal extent after the 1980s could be ascribed to the increase in potential evapotranspiration (PET) and is consistent with the negative trend in SPEI value over the six sub-regions. The apparent increase is mainly attributed to the increase in moderate and severe droughts area rather than extreme drought areas. The spectral analysis further reveals that inter-annual drought variability with periodicities less than 8 years dominates in all sub-regions of Equatorial East Africa, which is associated with the critical role of El-Niño in driving the drought variations in EEA.

Respective contributions of precipitation and potential evapotranspiration to long‐term changes in global drought duration and intensity

AbstractClimate change has resulted in an increase in drought in most global land areas, mainly due to a decrease in regional precipitation (P) or an increase in potential evapotranspiration (PET) induced by climate warming. However, knowledge on the contributions of P and PET to long‐term changes in global drought duration and intensity is still limited. In this study, we quantitatively analysed the respective contributions of P and PET to long‐term drought duration and intensity on a global scale, using standardized precipitation evapotranspiration index (SPEI) and different inputs of P and PET. The results showed that the mean drought duration and intensity experienced an increasing trend in most global land areas during 1950–2020, especially in western United States, eastern Amazon, Mediterranean region, Africa, western Asia, and northeastern Asia. The contributions of P and PET to historical drought evolution vary from regions. The results show that while increasing PET has extensive contribution to drought increase, regional increases in long‐term drought duration and intensity are largely determined by the variability in P, and the contribution of P to the increase in long‐term drought can even reach 100%. This study has great implications in improving physical understanding of long‐term drought evolution under climate change.

Impacts of Climate and Land Use/Cover Change on Water Yield Services in the Upper Yellow River Basin in Maqu County

The upper Yellow River Basin is an important ecological security barrier and a water conservation area in northwest China. The sustainability of its water yield services has generated much concern and debate. Spatial and temporal patterns of water yield factors are considered to be important scientific data. Therefore, the climate and land data of the upper Yellow River Basin in Maqu County are studied. Water yield for the period 1990–2020 was estimated using the water yield module in the InVEST model. Impacts and contribution weights of climate and land use/cover change on regional water yield were also quantified under 12 scenarios. The results indicate that (1) the average water yield in Maqu County has fluctuated and increased in the past 30 years. The increase in rainfall was more pronounced than the increase in potential evapotranspiration. Grassland areas continue to increase and unutilized land areas continue to decrease. (2) The average water yield for different types of land use during this period also varied. It showed grassland > unutilized land > forest > construction land > waterbody > cropland. (3) Climate change has a greater impact on water yield in Maqu County and further increases its contribution to regional water yield. The impact of land use/cover change was smaller and the contribution was smaller.

Driving factors and changes in components of terrestrial water storage in the endorheic Tibetan Plateau

Terrestrial water storage (TWS) in the endorheic Tibetan Plateau (ETP) increased from 2002 to 2012 but decreased in 2012–2016. This study used Gravity Recovery and Climate Experiment (GRACE) data and Global Land Data Assimilation System (GLDAS) data to analyse TWS changes in the ETP in 2012 from increasing to decreasing. The results showed that these TWS changes could be divided into two stages. From April 2002 to August 2012, TWS increased at a rate of 4.43 Gt/yr from the GRACE-Mascons and 1.11 Gt/yr from the GRACE-SH, whereas after September 2012, it declined at a rate of-5.62 Gt/yr from the GRACE-Mascons and −6.99 Gt/yr from the GRACE-SH. The increase in lake water storage (LWS) (7.98 Gt/yr) was higher than the loss of other components from 2002 to 2012, therefore, the LWS gradually dominated the increase in TWS. However, the soil moisture storage (SMS) decreased more significantly (-5.27 Gt/yr) than the increase in LWS (<1 Gt/yr) during 2012–2016, accounting for 66% of the decrease in TWS in the ETP. From a water balance perspective, the relationship between precipitation (P) and evapotranspiration determined the region’s changes in TWS. It was found that 90% of the decrease in TWS in the ETP during 2012–2016 was attributed to an increase in potential evapotranspiration (PET), whereas 7% was attributed to a decrease in P. Thus, climate change (P and PET) accounted for 97% of the TWS reduction during 2012–2016. Furthermore, 3% of the decrease in TWS in the region was attributed to land surface changes.

Impact of Climate Change on Soil Water Content in Southern Saskatchewan, Canada

The main objective of this research was to understand the effects of climate change on soil water content (SWC) across the Qu’Appelle River basin in southern Saskatchewan, Canada. The Soil and Water Assessment Tool (SWAT) and output from 11 high-resolution (0.22°) regional climate models (RCM) were used over three 30-year periods: the near future (2021–2050) and distant future (2051–2080) and the historical reference (1975–2005). The RCM data are from the CORDEX North American domain, which employs the RCP8.5 high-emission scenario. SWC was modeled at the hydrological response units (HRU) level and at daily and monthly (warm season only) intervals for 2015–2020. The model was calibrated and validated using SUFI-2 in SWAT-CUP based on observations for streamflow and SWC, including measured data and Soil Moisture Active Passive (SMAP) Level 4 for surface (up to 5 cm deep) soil moisture. Values of the Nash–Sutcliffe model efficiency (NS) ranged from 0.616 and 0.784 and the coefficient of determination (R2) was 0.8 for calibration and 0.82 for validation. Likewise, the correlation coefficients between ground measurements and SWAT were 0.698 and 0.633, respectively. Future climate forcing of the calibrated SWAT model revealed that warmer and drier growing seasons will prevail in the region. Similarly, the ensemble of all RCMs indicated that the mean temperature will increase by 2.1 °C and 3.4 °C for the middle and late periods, respectively, along with a precipitation increase of 10% and 11.2%. SWC is expected to decrease with an increase in potential evapotranspiration, despite an increase in precipitation. Likewise, the annual SWC is expected to decrease by 3.6% and 4% in the middle and late periods, respectively. The monthly SWC changes showed the highest decreases (5.4%) in April in the late period. The spatial pattern of SWC for 11 RCMs was similar such that the northwest and west of the river basin are wetter than the south and east. SWC projections suggest that southern Saskatchewan could experience significant SWC deficiencies in the summer by the end of this century.

Changes in the drought condition over northern East Asia and the connections with extreme temperature and precipitation indices

Drought conditions are experiencing substantial changes due to global warming, but the contributions of changes in temperature, precipitation, and associated extremes to drought severity at the regional scale remain an important topic for climate change research. Northern East Asia (NEA) has experienced frequent climate extremes and is very sensitive and vulnerable to climate change. We analyze the spatiotemporal variations of the Standardized Precipitation-Evapotranspiration Index (SPEI) and 7 ETCCDI extreme climate indices (ECIs), the relationship between SPEI and ECIs, and the mechanism for SPEI changes during 1979–2018. Observations indicate a significant increasing trend in drought severity in NEA. Warm-related ECIs show a similar increasing trend, while precipitation-related ECIs (heavy precipitation days and extreme precipitation intensity) display no significant trend. Correlation analysis indicates that the intensification of drought in NEA is strongly related to the changes in average temperature and related ECIs, while the correlation with precipitation and related ECIs is weak and insignificant. A coupled model (CSIRO-MK3.6.0) simulation driven by realistic external forcing reasonably reproduced the observed NEA SPEI changes and the relationships with temperature, precipitation, and the related-ECIs. Attribution analysis is further conducted using the model simulations. The increased severity of NEA drought is attributed to remarkable increases in potential evapotranspiration (PET), caused by increases in surface net radiation and the vapor pressure deficit (VPD), and the VPD makes a more significant contribution to the decrease in SPEI. Increased PET intensifies the drought condition in NEA even though the moisture supply (precipitation) experiences no decrease trends during 1979–2018. The strong warming and increase in warm-related ECIs drive increases in the VPD, intensifying the evaporative demand and amplifying the drought conditions in NEA. Our findings highlight the connections between drought risks and intense warm extremes at regional scales and the potential role of external radiative forcing in causing these changes. • A significant increasing trend in drought severity is observed over northern East Asia in the recent four decades. • Drought in northern East Asia closely linked to changes in temperature and related extremes. • Coupled model driven by realistic external forcing has good capability in reproducing the drought change. • Increased evaporative demand leads to amplification of the drought conditions in northern East Asia under global warming.

Changing Water Resources Under El Niño, Climate Change, and Growing Water Demands in Seasonally Dry Tropical Watersheds

AbstractThe wet‐dry tropics of Central America are characterized by long dry seasons, during which communities often struggle for water. High interannual rainfall variability, driven in parts by the El Niño Southern Oscillation (ENSO), increases these challenges. Further, climate change projections indicate that the region will likely become drier. However, research on impacts on water resources at the watershed scale is limited in the region—yet this information is essential for water managers. Therefore, in this research, we quantified the potential impacts of ENSO and four different climate change scenarios on water resources in two watersheds in the wet‐dry tropics of Guanacaste, Costa Rica, using a hydrological model (Water Evaluation and Planning Tool [WEAP]). Given that the watersheds are human used, we also explored different water demand scenarios. Modeling results indicated that an extreme El Niño can reduce groundwater recharge and streamflow by ∼60% relative to ENSO neutral. For 2075–2100, modeling results indicated that while potential evapotranspiration increases, actual evapotranspiration decreases due to limited water availability. Further, climate change may lead to reductions of mean annual streamflow and groundwater recharge by 40%–45% and 26%–28%, respectively, in comparison to the historical baseline. Importantly, high population growth could further hasten potentially irreversible groundwater storage declines. On the other hand, reduction of per‐capita water demand could slow down, or even reverse, the decline of groundwater storage.

Modeling Climate Change Impacts on Water Balance of a Mediterranean Watershed Using SWAT+

The consequences of climate change on food security in arid and semi-arid regions can be serious. Understanding climate change impacts on water balance is critical to assess future crop performance and develop sustainable adaptation strategies. This paper presents a climate change impact study on the water balance components of an agricultural watershed in the Mediterranean region. The restructured version of the Soil and Water Assessment Tool (SWAT+) model was used to simulate the hydrological components in the Sulcis watershed (Sardinia, Italy) for the baseline period and compared to future climate projections at the end of the 21st century. The model was forced using data from two Regional Climate Models under the representative concentration pathways RCP4.5 and RCP8.5 scenarios developed at a high resolution over the European domain. River discharge data were used to calibrate and validate the SWAT+ model for the baseline period, while the future hydrological response was evaluated for the mid-century (2006–2050) and late-century (2051–2098). The model simulations indicated a future increase in temperature, decrease in precipitation, and consequently increase in potential evapotranspiration in both RCP scenarios. Results show that these changes will significantly decrease water yield, surface runoff, groundwater recharge, and baseflow. These results highlight how hydrological components alteration by climate change can benefit from modelling high-resolution future scenarios that are useful for planning mitigation measures in agricultural semi-arid Mediterranean regions.

Expansion of drylands in China with an additional half a degree warming

AbstractTo contribute a more ambitious target of Paris Agreement, that is, limiting global warming to 1.5°C instead of 2.0°C above preindustrial levels, it is essential to quantitatively reveal regional impacts of an additional 0.5°C warming to inform climate policymaking. Based on bias‐corrected simulations of four models from the half a degree additional warming, prognosis and projected impacts (HAPPI), we examine how dry–wet condition may change in China at 1.5 and 2.0°C warming levels, focusing on the projected changes in the area of drylands. Results showed that China is projected to be dominated by a decrease Surface Wetness Index (SWI), due to a larger increase in potential evapotranspiration (PET) than precipitation, implying a drying signal, in both 1.5 and 2.0°C warming levels against a present‐day scenario. Correspondingly, an expansion of drylands is expected, the larger expansion with the higher warming level, with changes approximately 0.77 ± 2.02% in 1.5°C level, and 2.29 ± 2.69% in 2.0°C level, although there exists considerable intermodel variability. For an additional warming of 0.5°C, there is high confidence of the projected decrease of SWI and expansion of drylands, approximately 1.52 ± 0.77%. That is to say, limiting global warming to 1.5°C is suggested to robustly reduce the likelihood of emerging aridification compared to 2°C, and China might obtain considerable benefits in term of socio‐economic impacts related to the reduction of aridification. Thus, it is necessary for continued efforts to limit global warming to 1.5°C.

Watershed-Scale, Probabilistic Risk Assessment of Water Resources Impacts from Climate Change

A framework for the assessment of relative risk to watershed-scale water resources from systemic changes is presented. It is composed of two experiments, or pathways, within a Monte Carlo structure and provides quantification of prediction uncertainty. One simulation pathway is the no change, or null hypothesis, experiment, and the other provides simulation of the hypothesized system change. Each pathway uses a stochastic weather generator and a deterministic water balance model. For climate change impact analysis, the framework is calibrated so that the differences between thirty-year average precipitation and temperature pathway values reproduce climate trends. Simulated weather provides forcing for identical water balance models. Probabilistic time histories of differences in actual evapotranspiration, runoff, and recharge provide likelihood per magnitude change to water resources availability. The framework is applied to a semi-arid watershed in Texas. Projected climate trends for the site are a 3 °C increase in average temperature and corresponding increase in potential evapotranspiration, no significant change in average annual precipitation, and a semi-arid classification from 2011–2100. Two types of water balance model are used in separate applications: (1) monthly water balance and (2) daily distributed parameter. Both implementations predict no significant change, on average, to actual evapotranspiration, runoff, or recharge from 2011–2100 because precipitation is unchanged on average. Increases in extreme event intensity are represented for future conditions producing increased water availability during infrequent events.

Insight from CMIP6 SSP-RCP scenarios for future drought characteristics in China

In this paper, future drought characteristics (frequency, duration and intensity) over China are analysed by using four climate models from CMIP6 under the seven SSP-RCP (shared socioeconomic pathway-representative concentration pathway) scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, SSP370, and SSP585) for three defined periods of 2021–2040 (near-term), 2041–2060 (mid-term) and 2081–2100 (long-term). The corresponding four climate models output from CMIP5 are also used to conduct a comparison analysis between CMIP5 and CMIP6 to address the improvements added to CMIP6 in terms of drought identification. The drought characteristics are identified by applying the standardized precipitation-evapotranspiration index (SPEI) at a 12-month timescale and run theory. The results show that CMIP6 has a robust capability to capture historical (1986–2005) drought characteristics. For the future period of 2021–2040, the decrease in precipitation and increase in potential evapotranspiration will lead to continuous dry conditions in the upper and middle Yangtze River basin and eastern Pearl River basin. Relative to the reference period, drought events will be more frequent and severe with longer durations in the Northwest River basins and middle Yangtze River basin. Furthermore, higher emissions signify a greater increase in drought frequency and intensity in the long-term period. Except for the SSP585 scenario, the lower emission scenario corresponds to the higher drought duration soon and in the mid-21st century (2021–2060). This finding is regarded as a “strange phenomenon”, which cannot be detected by the previous CMIP5-based emission scenarios (RCP2.6, RCP4.5 and the unlikely pathway RCP8.5). Therefore, additional “possible future”-based scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, and SSP370) should be included in extreme climate studies, especially for the near future and mid-21st century. Notably, compared with CMIP5, the reduced biases in drought characteristics are more likely associated with improvements in the representation of physical processes in climate models from CMIP6. The results of this study could provide a basis for the development of drought adaptation measures over China.