Effects of using air temperature as a proxy for potential evapotranspiration in climate change scenarios of Great Lakes basin hydrology

Hydrologic impacts of climate change are regularly assessed with hydrologic models that use air temperature as a proxy to compute potential evapotranspiration (PET). This approach is taken in the Large Basin Runoff Model (LBRM), which has been used several times for calculation of the runoff from the terrestrial part of the Great Lakes basin under climate change scenarios, with the results widely cited. However, a balance between incoming and outgoing energy, including the latent heat of evaporation, is a fundamental requirement for a land surface, and is not enforced under this approach. For calculating PET and evapotranspiration (ET) in climate change scenarios, we use an energy budget-based approach to adjusting the PET as an alternative that better satisfies conservation of energy. Using this new method, the increase in ET under enhanced greenhouse gas concentrations has reduced magnitude compared to that projected using the air temperature proxy. This results in either a smaller decrease in net basin supply and smaller drop in lake levels than using the temperature proxy, or a reversal to increased net basin supply and higher lake levels. An additional reason not to rely on a temperature proxy relation is that observational evidence demonstrates that the correlation between air temperature and ET (or PET) is restricted to the mean annual cycle of these variables. This brings into question the validity of air temperature as a proxy for PET when considering non-annual variability and secular changes in the climate regime.     

The Impacts of Climate Variability and Future Climate Change in the Nile Basin on Water Resources in Egypt

This paper describes the application of hydrologic models of the Blue Nile and Lake Victoria sub-basins to assess the magnitude of potential impacts of climate change on Main Nile discharge. The models are calibrated to simulate historical observed runoff and then driven with the temperature and precipitation changes from three general circulation model (GCM) climate scenarios. The differences in the resulting magnitude and direction of changes in runoff highlight the inter-model differences in future climate change scenarios. A 'wet' case, 'dry' case and composite case produced +15 (+12), -9 (-9) and + 1(+7) per cent changes in mean annual Blue Nile (Lake Victoria) runoff for 2025, respectively. These figures are used to estimate changes in the availability of Nile water in Egypt by making assumptions about the runoff response in the other Nile sub-basins and the continued use of the Nile Waters Agreement. Comparison of these availability scenarios with demand projections for Egypt show a slight surplus of water in 2025 with and without climate change. If, however, water demand for desert reclamation is taken into account then water deficits occur for the present-day situation and also 2025 with ('dry' case GCM only) and without climate change. A revision of Egypt's allocation of Nile water based on the recent low-flow decade-mean flows of the Nile (1981-90) shows that during this period Egypt's water use actually exceeded availability. The magnitude of 'natural' fluctuations in discharge therefore has very important consequences for water resource management regardless of future climate change.     

The effects of climate change on the water resources of the Geumho River Basin,Republic of Korea

Assessments of the variation and vulnerability of water resources due to climate change are essential for future planning in agriculture. In this study, the impacts and uncertainty associated with climate change on water resources in the Geumho River Basin were measured based on the relative change in the mean annual runoff and the aridity index. Statistically adjusted and downscaled multi-ensemble General Circulation Model (GCM) predicted rainfall and temperature data for three representative concentration pathways (RCPs) (RCP2.6, 4.5 and 8.5) were applied to two lumped parameter conceptual rainfall runoff models. The results revealed considerable uncertainty in the projected temperature, rainfall, potential evapotranspiration (PET), runoff and aridity index (AI). Additionally, temperature and rainfall were predicted to increase significantly in the future. The PET was projected to increase by a mean (range) of 9% (7–12%), 18% (9–30%) and 25% (8–49%), while the mean annual runoff was projected to change by a mean (range) of 1% (−33 to 40%), −9% (−47 to 27%) and −4% (−44 to 35%), in the 2030s, 2060s and 2090s, respectively. The AI was projected to decrease in the future, particularly for the RCP8.5. Overall, the results of this study indicate that climate change will most likely lead to lower water resource levels than are currently present in the Geumho River Basin.     

流域径流变化驱动力分析与研究——以祖厉河为例

根据祖厉河流域水文站实测资料序列,对流域径流变化影响因子进行分析表明:21世纪初年代径流量平均值与20世纪70年代相比较减少了42.2%,气候变化和人类活动是影响河川径流的主要因素。自20世纪70年代以来,伴随着流域气温的不断升高,流域水文循环条件的改变,年径流量呈现逐年递减趋势,相关分析表明两者之间呈显著负相关关系。同时,流域水利水保工程和跨流域引水提灌工程也是改变流域径流的主要因素,其对径流量的变化影响占到70%以上。     

基于SWAT模型的秦淮河流域气候变化水文响应研究

为了解气候变化对水文水资源的影响机理,以秦淮河流域为研究区构建SWAT模型,使用SWAT-CUP对模型进行参数敏感性分析、率定及验证,并采用任意假设法设计未来气候情景,分析温度及降雨变化对流域径流及实际蒸散发量的影响。结果表明:模型在月径流模拟中具有较高的精度,适用于秦淮河流域气候变化下的水文响应研究;气温降低或降雨量上升都会引起流域径流量增加,反之则减少;实际蒸散发量与降雨量正相关,而实际蒸散发量对气温变化的响应不明显;平水年径流量对降雨量变化的响应较强,枯水年径流量对温度变化的响应较强;枯水年实际蒸散发量对降雨量变化的响应较强。     

气候变化对汉江上游径流特征影响预估

为了预测水文站逐月径流,对该流域水资源变化进行评估,运用小波神经网络建立汉江上游流域气象因子与径流过程模拟预测模型,并依据未来气候变化增量情景,对石泉水文站以上流域径流变化响应过程进行不同时间尺度分析。由已知汉江上游流域的月降水量和月平均温度,经小波神经网络自动“学习”训练获得石泉水文站精度较高的逐月径流数据。模拟计算结果表明:在不同未来气候变化设定情景下,该区域径流变化过程较为明显,年平均径流量最大变化范围为-34.7% ~ 21.4%。在降雨量不变、气温升高的情况下,年平均径流的响应变化范围为-5.1% ~ -13.3%。温度升高引起冬季径流增加较为明显,春季及秋季径流则存在减小趋势,秋季明显减少,而降雨量变化对夏季径流的影响最显著。     

Assessing Impacts of Conservation Measures on Watershed Hydrology Using MIKE SHE Model in the Face of Climate Change

Climate change triggers changes in temperature, precipitation, evapotranspiration, etc. and has a significant impact on water resources in many regions. Considering the increasing scarcity of water as a result of climate change, conservation of water and groundwater recharge have become crucial factors for water resources planning and management. In this paper, an attempt is made to study the detailed hydrological behaviour of a treated watershed using physically based distributed hydrological modelling system MIKE SHE to assess the impact of conservation measures on watershed hydrology considering future climate change. Three hypothetical management scenarios are simulated for the period 2010–2040. RegCM4 regional climate model is used in the study for RCP 4.5 and RCP 8.5 scenarios. Detailed hydrological water balance is extracted for individual years from 1979 to 2009 to compare relevant components. The evaluation for base period shows 10.06% reduction in surface runoff and 11.33% enhancement in groundwater recharge. Further simulation with RCP 4.5 and RCP 8.5 scenarios show notable reduction in surface runoff and increase in groundwater recharge. The structures in the micro-watershed influence the surface runoff and increase infiltration into the soil, resulting in higher groundwater recharge. MIKE SHE simulations for various structures management scenarios establish the role of conservation measures in reducing surface runoff and enhancing groundwater recharge under substantial effect of climate change. The results will assist in decision-making on watershed development plans in quantitative terms, including planning for water conservation measures in the face of climate change.

     

A Water Budget Model for the Yun-Lin Plain,Taiwan

A water budget model is proposed to estimate the infiltration, runoff, evapotranspiration and recharge in vadose zone and apply to a case study. The instantaneous redistribution of infiltrated water is assumed to be uniform and a linear relationship between evapotranspiration and effective saturation is imposed. Infiltration is described by Philip's solution in conjunction with the time compression approximation method during rainfall. Runoff occurred when rainfall rate exceeds soil-infiltrating rate. The soil profile drainage was determined by evapotranspiration and recharge. Cumulative infiltration, runoff, evapotranspiration and recharge are estimated with different climate conditions and different soil hydraulic properties during simulating period. Analysis shows that initial effective saturation affects the estimated results in this water budget model in the short or mid-term simulations while not in long-term simulations. The climatic conditions of Yun-Lin plain area, Taiwan from 1991 to 1997 are used by referring to hydrological and hydrogeological parameters to provide the computational procedures of this study for estimating recharge. Results showed that the amount of annual recharge was affected by the amount of annual rainfall and soil properties.     

基于Budyko弹性系数法的佳芦河流域径流变化归因识别

气候变化和人类活动对径流的影响是一个综合过程,因此径流动态变化及其归因识别和定量表征对区域水资源开发管理至关重要.以佳芦河流域为研究区,选用Mann-Kendall趋势检验法、有序聚类法等分析了研究区水文要素的主要变化特征;采用基于Budyko水热耦合平衡理论的弹性系数法,定量分析了径流深变化对各驱动因素的响应程度.结...     

Future Hydrological Drought Analysis Considering Agricultural Water Withdrawal Under SSP Scenarios

Hydrological drought is assessed through river flow, which depends on river runoff and water withdrawal. This study proposed a framework to project future hydrological droughts considering agricultural water withdrawal (AWW) for shared socioeconomic pathway (SSP) scenarios. The relationship between AWW and potential evapotranspiration (PET) was determined using a deep belief network (DBN) model and then applied to estimate future AWW using projections of the twelve global climate models (GCMs). 12 GCMs were bias-corrected using the quantile mapping method, climate variables were generated, and river flow was estimated using the soil and water assessment tool (SWAT) model. The standardized runoff index (SRI) was used to project the changes in hydrological drought characteristics. The results revealed a higher occurrence of severe droughts in the future. Droughts would be more frequent in the near future (2021–2060) than in the far future (2061–2100) and more severe when AWW is considered. Droughts would also be more severe for SSP5-8.5 than for SSP2-4.5. The study revealed that the increased PET due to rising temperatures is the primary cause of the increased drought frequency and severity. The AWW will accelerate the drought severities in the future in the Yeongsan River basin.

     

Climate Change and Hydrological Response in the Trans-State Oologah Lake Watershed–Evaluating Dynamically Downscaled NARCCAP and Statistically Downscaled CMIP3 Simulations with VIC Model

Statistically and dynamically downscaled climate projections are the two important data sources for evaluation of climate change and its impact on water availability, water quality and ecosystems. Though bias correction helps to adjust the climate model output to behave more similarly to observations, the hydrologic response still can be biased. This study uses Variable Infiltration Capacity (VIC) model to evaluate the hydrologic response of the trans-state Oologah Lake watershed to climate change by using both statistically and dynamically downscaled multiple climate projections. Simulated historical and projected climate data from the North American Regional Climate Change Assessment Program (NARCCAP) and Bias-Corrected and Spatially Downscaled–Coupled Model Intercomparison Phase 3 (BCSD-CMIP3) forced the hydrologic model. In addition, different river network upscaling methods are also compared for a higher VIC model performance. Evaluation and comparison shows the following the results. (1) From the hydrologic point of view, the dynamically downscaled NARCCAP projection performed better, most likely in capturing a larger portion of mesoscale-driven convective rainfall than the statistically downscaled CMIP3 projections; hence, the VIC model generated higher seasonal streamflow amplitudes that are closer to observations. Additionally, the statistically downscaled GCMs are less likely to capture the hydrological simulation probably due to missing integration of climate variables of wind, solar radiation and others, even though their precipitation and temperature are bias corrected to be more favorably than the NARCCAP simulations. (2) Future water availability (precipitation, runoff, and baseflow) in the watershed would increase annually by 3–4 %, suggested by both NARCCAP and BCSD-CMIP3. Temperature increases (2.5–3 °C) are much more consistent between the two types of climate projections both seasonally and annually. However, NARCCAP suggested 2–3 times higher seasonal variability of precipitation and other water fluxes than the BCSD-CMIP3 models. (3) The hydrologic performance could be used as a potential metric to comparatively differentiate climate models, since the land surface and atmosphere processes are considered integrally.     

黄淮海流域实际蒸散发时空演变规律分析

蒸散发是气候系统能量循环和水分循环的关键要素,探究黄淮海流域实际蒸散发的演变规律及其影响因素对深入理解该区域水循环对气候变化的响应具有重要意义。基于1980—2018年黄淮海流域的GLEAM蒸散发产品数据、气象数据和NDVI数据,采用线性回归法、Mann-Kendall检验及相关性分析等方法,分析了实际蒸散发的时空演变规律及其影响因素。结果表明：GLEAM产品的计算值在黄淮海流域的验证精度较好,流域内多年平均实际蒸散发量为474 mm,呈显著上升趋势。实际蒸散发的空间变化范围是183～708 mm,空间差异显著,呈现从东南向西北方向递减的趋势,季节的空间分布与年际分布特征基本一致。实际蒸散发与NDVI均呈显著正相关关系,与降水和气温以正相关关系为主。黄淮海流域降水变化不明显,气温显著升高,NDVI增加是流域内实际蒸散发量显著上升的主要原因。     

Impacts of Hydrological Changes on Annual Runoff Distribution in Seasonally Dry Basins

Runoff is expected to change due to climate and land use change. Because it constitutes a large component of the terrestrial water budget, we need to develop new policies for managing regional water resources. To do so, we must first attribute changes in the natural flow regime to either climate or land use change. In this context, the Budyko’s curve has previously been adopted to separate the impacts of climate and land use change on runoff by using long term hydrological variables. In this study, a framework based on Fu’s equation (which describes Budyko’s curve) is used to separate the impacts of climate and land use change on annual runoff distributions. Specifically, this framework is based on a recently developed method to obtain annual runoff probability density function (pdf) in seasonally dry basins—such as those in Mediterranean regions—from climate statistics and Fu’s equation parameter ω. The effect of climate change is captured through variations in the first order statistics of annual rainfall and potential evapotranspiration, while land use change is represented by changes in Fu’s equation parameter ω. The effects of these two drivers (i.e., climate and land use change) are analyzed by reconstructing the annual runoff pdfs for the current period and for likely future scenarios, based on predictions from global circulation models and urbanization trajectories. The results show that climate change can lead to a strong reduction in mean annual runoff, a shift of the runoff pdf toward lower values, and a decrease in its variance. Concurrent changes in climate and land use almost always result in a reduction in the mean annual runoff, due to the greater impact of climate change on the runoff pdf.

     

Application of SEBAL and Markov Models for Future Stream Flow Simulation Through Remote Sensing

Watershed hydrology, including the volumes of stream flow is widely considered to be influenced by global climate change. Traditional studies using the (GWLF) model to estimate stream flows have relied on evapotranspiration cover coefficient (Kc) obtained from published references. Other factors, such as future land-use status and evapotranspiration (ET) change, are usually not considered. This study aims to improve on traditional studies by including remote sensing techniques to estimate the Kc, as well as integrating the SEBAL model, the CGCM1 model, and the Markov model to predict land-use and ET changes. The chosen study area was in the north of Taiwan. The processes include land-use classification using hybrid approach and Landsat-5 TM images, a comparison of stream flow simulations using the GWLF model with two Kc values derived from remote sensing and traditional methods, and finally the prediction of future land-use and Kc parameters for assessing the effect of land-use change and ET change. The results indicated that the study area was classified into seven land-use types with 89.09% classification accuracy. The stream flows simulated by two estimated Kcs were different, and the simulated stream flows using the remote sensing approach presented more accurate hydrological characteristics than a traditional approach. In addition, the consideration of land-use change and ET change indeed affected the predicted stream flows under climate change conditions. These results imply that the integration of remote sensing, the SEBAL model, the CGCM1 model, and the Markov model is a feasible scheme to predict future land-use, ET change, and stream flow. Therefore, these models will improve future studies of predictions in water resource management and global environmental change.     

不同蒸散发产品在汉江流域的比较研究

蒸散发是流域水循环和能量循环的重要环节,准确估算蒸散发对流域水循环研究具有重要意义,同时也可以为流域水资源优化配置和可持续利用提供支撑。利用汉江流域观测的逐月降水数据、径流数据以及重力卫星(GRACE)反演的流域蓄水量变化数据计算水量平衡蒸散发(ET_WB),以ET_WB为标准在月尺度上评估4类9种不同蒸散发产品(陆面模式产品ET_clm、ET_noah、ET_mos、ET_vic;再分析数据产品ET_jra;基于模型树集的通量观测产品ET_jung和基于能量平衡的诊断模型产品ET_modis、ET_PML、ET_Zhangke)在汉江流域的适用性。结果表明基于模型树集的通量观测产品和基于能量平衡的诊断模型产品精度较好,再分析产品次之,陆面模式产品(除ET_clm)较差。ET_jung、ET_modis和ET_clm在月尺度上与ET_WB有着较好的相关性,结果误差相对较小;ET_noah、ET_mos、ET_vic结果误差相对较大。该研究结果可以为汉江流域水循环研究和南水北调中线工程管理提供科学参考。     

An Integrated Approach for Partitioning the Effect of Climate Change and Human Activities on Surface Runoff

Climate change and human activities have been identified as the two main reasons for the change in runoff. To better understand the factors causing runoff change, this paper develops an integrated approach which combined the elasticity coefficient approach (including a non-parametric model and six Budyko framework based models) and the hydrological modelling approach (using SIMHYD models) for partitioning the impacts of climate change and human activities on surface runoff. The Guanzhong River Basin(GRB), which is the sub-basin of the Wei River basin in China is chosen as the study area. In this study, trends in runoff, rainfall and potential evapotranspiration (PET) from 1958 to 2008 are analyzed using the Mann-Kendall test and change-points in the annual runoff from 1958 to 2008 are sought using the Fu formula, Mann-Kendall test and double mass curve. The calibrated and validated rainfall-runoff model SIMHYD is used to simulate the runoff in the GRB during 1958–2008. Seven different methods are used to calculate the elasticity coefficient and then the elasticity coefficient methods are used to evaluate the contribution of climate change and human activities. Combining all these results, the contribution of climate change and human activities to runoff change is 34.1?~?47.3 and 52.7?~?65.9 %, respectively. The study provides scientific foundation for understanding the causes of water resources decrease and significant information for water resources management under the influence of climate change and human activities.     

Potential Impact of Climate Change on Rainfall Intensity-Duration-Frequency Curves in Roorkee,India

Intensification and frequency of hydrologic events are attributed to climate change and are expected to increase in coming future. Intensity-Duration-Frequency (IDF) curves quantify the extreme precipitation and are used extensively to assess the return periods of rainfall events. It is expected that climate change will modify the occurrence of extreme rainfall events. Thus a need of updating IDF curves arises under the climate change scenario. This paper aims at updating the IDF curves for a typical Indian town using an ensemble of five General Circulation Models (GCMs) for all the Representative Concentration Pathways (RCP) scenarios. Sub-daily maximum intensities (15-, 30-, 45-, 60-, 120-, and 180 min) were obtained from the observed records. Equidistance quantile method was used to study the relationships between the historical and projected GCM data, and the historical GCM and observed sub-daily data. This relationship was used to obtain projected sub-daily intensities. The IDF curves were developed using observed and projected data. Analysis of the curves indicated increase in precipitation intensities for all the RCP scenarios. It was also found that intensities of all return periods increases with intensifying RCP scenarios. The variation in the intensities across the GCMs was attributed to the driving forces considered in a particular GCM.     

Water Resource Availability in Three Catchments of Swaziland under Expected Climate Change

Abstract

The greenhouse gases (CO₂, CH₄, N₂O, HFCs, PFCs, and SF₆) concentrations in the atmosphere have increased very much since the industrial revolution. The greenhouse gas effect has been projected to cause a global average temperature increase on the order of 1.4 to 5.8°C over the period of 1990 to 2100. The global average annual precipitation is projected to increase during the 21^st century due to the greenhouse effect. The impact of climate change on hydrology and water resources in the three catchments of Swaziland (Komati, Mbuluzi and Ngwavuma) has been evaluated using General Circulation Model results (rainfall, potential evapotranspiration, air temperature etc.) as inputs to a rainfall runoff model. Three General Circulation Models (GCMs) namely: Canadian Climate Change Equilibrium (CCC-EQ); Geophysical Fluid Dynamics Laboratory (GFDL) and United Kingdom Transient Resilient (UKTR) were found appropriate for use to project the temperature and precipitation changes for Swaziland for year 2075. This information was used to generate the temperature, precipitation and potential evapotranspiration values for the three catchments for year 2075 which was input into a calibrated WatBall rainfall runoff model. Simulation results without taking into consideration of water use projections show that there will be high flows during the summer months but low flows during the winter months. Simulation results after taking into consideration of water use projections show a water deficit from June to September in both the Komati, and Ngwavuma catchments and a water deficit from May to September in the Mbuluzi catchment. This means that the environmental water needs and Swaziland's water release obligation in the three catchments to South Africa and Mozambique will not be met during the winter months under expected climate change conditions.     

由气候变化看天山西部流域水文特性的改变及水文趋势预测

以天山西部流域为代表,分析了47 a来气温、降水和河流径流的变化趋势,论述了天山西北地区河流在气候变化条件下的水文异常现象与水文特性改变的事实,并对未来的水文变化趋势进行了初步探讨和预测分析。分析结果显示:从气候变化的角度认识河流水文特性的改变,并以此为基础来分析水文趋势可能发生的变化,是很有必要的。     

气候变化对嘉陵江流域水资源量的影响分析

 嘉陵江是长江的最大支流,流域面积约16万km2。针对2050,2100年不同的气候变化情景,选取较为不利的参数组合,根据降水、气温、湿度、风速、日照等气候要素的变化,建立潜在蒸发量模型计算流域的潜在蒸发量（ET0）,再根据流域内植被的蒸散发系数（Kc）,计算流域的面平均蒸散发量（ETc）。并利用流域面平均降水量减去径流深得到流域的实际蒸散发量,对计算的流域面平均蒸散发量进行验证。对不同的水平年利用降水的预测成果（气候变化情景不同具有不同的降水量预测成果）及计算流域的面平均蒸散发量,根据水量平衡模型分析计算气候变化对嘉陵江流域水量的影响。结果表明：不利条件下2050年年径流将减少23.0%～27.9%;2100将减少28.2%～35.2%;2050,2100年平均年径流分别相当于目前7年一遇和12年一遇的干旱年。由此说明,气候变化对流域内的水资源量影响十分显著。 