Analysis of the effect of climate change on the Nakdong river stream flow using indicators of hydrological alteration

This study models the effect of climate change on runoff in southeast Korea using the TANK conceptual rainfall-runoff model. The results are assessed using the indicators of hydrological alteration (IHA) developed by U.S. Nature Conservancy. Future climate time series are obtained by scaling historical series, provided by four global climate models (GCMs, IPCC, 2007) and three greenhouse gas (GHG) emissions scenarios (IPCC, 2000), to reflect a maximum increase of 3.6 °C in the average surface air temperature and 33% in the annual precipitation. To this end, the spatio-temporal change factor method is used, which considers changes in the future mean seasonal rainfall and potential evapotranspiration as well as the daily rainfall distribution. In this study, the variance range for precipitation is from +3.55% to +33.44% compared to the present for years between 2071 and 2100. The variance range for the daily mean temperature is estimated between +1.59 °C and +3.58 °C. Although the simulation results from different GCMs and GHG emissions scenarios indicate different responses of the flows to the climate change, the majority of modeling results show that there will be more runoff in southeast Korea in the future. According to the analysis results, the predicted impacts of hydrological alteration caused by climate change on the aquatic ecosystem are as follows: 1) an increase in the availability of aquatic ecosystem habitats in Nakdong River in future summers and winters, 2) an increase in stress on the aquatic ecosystem due to extremely high stream flow, 3) an increase in the stress duration of flood events for the Nakdong River downstream and 4) an increase in aquatic ecosystem stress caused by rapid increases or decreases in stream flow.     

Spatio-temporal effect of climate and land-use change on water balance of the Ganga river basin

The assessment of climate and land-use transformations upon the hydrologic response is crucial for decision-makers to accomplish various adaptation strategies. The Regional Climate Models (RCMs) have been extensively employed to study the impact of climate change on various hydrologic components. However, these climate models are subjected to a large number of uncertainties, which demands a careful selection of an appropriate climate model. To rationalize such uncertainties and select suitable models, a multi-criteria ranking technique has been employed. Ranking of RCMs has been done on its capability to simulate hydrologic components, i.e., simulations of the surface runoff by employing Soil Water Assessment Tool (SWAT), exercising Entropy, and PROMETHEE-2 approach. The spatial extent of changes in the hydrologic components is examined over the Ganga river basin, using the top three ranked RCMs, for a period from January 2021-December 2100. For the monsoon months (June-September), the future annual mean surface runoff will decrease substantially (−50% to −10%), while the flows for post-monsoon months (October-December) are projected to increase (10–20%). Extremes are noted to increase during the non-monsoon months, while a substantial decrease in medium events is also highlighted. Snow-melt is projected to increase during the months of November-March (50% to 400%). Major loss of recharge is expected to occur in the central part of the basin. The investigation presents not only a reliable impact assessment but also the valuation of future alterations in individual hydrological components and will furnish the administrators with substantive information, a prerequisite to formulating ameliorative policies.     

Analysis of spatio-temporal evolution of droughts in Luanhe River Basin using different drought indices

Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index(SPEI) and standardized precipitation index(SPI) at three- and six-month time scales and the self-calibrating Palmer drought severity index(sc-PDSI) were calculated to evaluate droughts in the study area. Temporal variations of the drought severity from 1960 to1989 were analyzed and compared based on the results of different drought indices, and some typical drought events were identified. Spatial distributions of the drought severity according to the indices were also plotted and investigated. The results reveal the following: the performances of different drought indices are closely associated with the drought duration and the dominant factors of droughts; the SPEI is more accurate than the SPI when both evaporation and precipitation play important roles in drought events; the drought severity shown by the sc-PDSI is generally milder than the actual drought severity from 1960 to 1989; and the evolution of the droughts is usually delayed according to the scPDSI. This study provides valuable references for building drought early warning and mitigation systems in the Luanhe River Basin.     

Assessment of future climate change impacts on hydrological behavior of Richmond River Catchment

This study evaluated the impacts of future climate change on the hydrological response of the Richmond River Catchment in New South Wales (NSW), Australia, using the conceptual rainfall-runoff modeling approach (the Hydrologiska Byrans Vattenbalansavdelning (HBV) model). Daily observations of rainfall, temperature, and streamflow and long-term monthly mean potential evapotranspiration from the meteorological and hydrological stations within the catchment for the period of 1972–2014 were used to run, calibrate, and validate the HBV model prior to the streamflow prediction. Future climate signals of rainfall and temperature were extracted from a multi-model ensemble of seven global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 3 (CMIP3) with three regional climate scenarios, A2, A1B, and B1. The calibrated HBV model was then forced with the ensemble mean of the downscaled daily rainfall and temperature to simulate daily future runoff at the catchment outlet for the early part (2016–2043), middle part (2044–2071), and late part (2072–2099) of the 21st century. All scenarios during the future periods present decreasing tendencies in the annual mean streamflow ranging between 1% and 24.3% as compared with the observed period. For the maximum and minimum flows, all scenarios during the early, middle, and late parts of the century revealed significant declining tendencies in the annual mean maximum and minimum streamflows, ranging between 30% and 44.4% relative to the observed period. These findings can assist the water managers and the community of the Richmond River Catchment in managing the usage of future water resources in a more sustainable way.     

Forecasting impacts of climate change on Great Lakes surface water temperatures

Temperature influences the rates of many ecosystem processes. A number of recent studies have found evidence of systematic increases in Great Lakes surface water temperatures. Our study aims to construct empirical relationships between surface water temperatures and local air temperatures that can be used to estimate future water temperatures using future air temperatures generated by global climate models. Remotely sensed data were used to model lake-wide average surface water temperature patterns during the open-water period in Lakes Superior, Huron, Erie, and Ontario. Surface water temperatures typically exhibit linear warming through the spring, form a plateau in mid-summer and then exhibit linear cooling in fall. Lake-specific warming and cooling rates vary little from year to year while plateau values vary substantially across years. These findings were used to construct a set of lake-specific empirical models linking surface water temperatures to local air temperatures for the period 1995–2006. Hindcasted whole-lake water temperatures from these models compare favourably to independently collected offshore water temperatures for the period 1968–2002. Relationships linking offshore water temperatures to inshore water temperatures at specific sites are also described. Predictions of future climates generated by the Canadian Global Climate Model Version 2 (CGCM2) under two future greenhouse gas emission scenarios are used to scope future Great Lakes surface water temperatures: substantial increases are expected, along with increases in the duration of summer stratification.     

The socio-economic impacts of climate change on water resources in South Africa

Using a computable general equilibrium approach, this study investigates the economy-wide impact of reductions in water resources in South Africa due to climate change. The simulation results show a potentially general deterioration in household welfare. Poor households are the most vulnerable. Short-run policy simulations suggest that this vulnerability can be reduced through welfare policies that maintain food consumption levels for households in the two lowest income quintiles.     

Effects of climate and land use changes on stream flow of Chitral river basin of northern highland Hindu-Kush region of Pakistan

Adverse impacts of climate change on the ecosystem have been a significant concern in the last decades. However, the studies related to the impacts of climate change on water resources, especially in northern Pakistan are of great importance as this region is the main supplier of freshwater to the downstream areas. So, the present study was carried out in Chitral River Basin (CRB) to investigate the long term climatic and topographic changes. Spatiotemporal datasets from MODIS Land Cover Type product (MCD12Q1) from 2001 to 2018, ground-based observational climatic and hydrological data were used. Moreover, the Mann-Kendall trend test, linear regression analysis, correlation, and Sen’s slope values for the mean annual and seasonal flows were assessed. The acquired results show that land use changes are the key non-natural factors in transforming the ecological and hydrological processes of CRB. The mixed and evergreen forest, shrubland, savannas, and barren land respectively decreased from 0.07 to 0.03%, 0.07 to 0.05%, 3.64 to 3.25%, and 70.10 to 67.17%, from 2001 to 2018. In addition, a considerable increment in snow cover from 8.79% to 10.71%, and slight increment in grasslands, wetlands, and croplands were also found between the period of observation. In addition, total annual precipitation and mean annual stream flow showed slight upward trends. Annual increment in total rainfall and snow covered area could be the possible reasons for the observed increased river flow.     

Optimal water allocation at different levels of climate change to minimize water shortage in arid regions (Case Study: Zayandeh-Rud River Basin,Iran)

Climate change is one of the most important factors influencing the future of the world's environment. The most important impacts of climate change are changes in water supply and demand in different regions of the world. In this study, different climate change patterns in two RCP4.5 and RCP8.5 emission scenarios (RCP: Representative Concentration Pathway), were adopted for the Zayandeh-Rud River Basin, Iran, through weighting of GCMs (General Circulation Models). These climate change patterns are including ideal, medium, and critical patterns. Using the LARS-WG model (Long Ashton Research Station Weather Generator), the outputs of the GCMs were downscaled statistically and the daily temperature and precipitation time series were generated from 2020 to 2044. Then, based on this information, the inflow volume into the Zayandeh-Rud Reservoir was predicted by the IHACRES model (Identification of unit Hydrograph and Component flows from Rainfall, Evaporation and Streamflow) and the agricultural water demand was also estimated based on future evapotranspiration. Finally, using GAMS (General Algebraic Modeling System) software, water resources in this basin were allocated based on the basic management scenario (B) and the water demand management scenario (D). The results showed that the average monthly temperature will increase by 0.6 to 1.3 °C under different climate change patterns. On the other hand, on the annual basis, precipitation will decrease by 6.5 to 31% and inflow volume to the Zayandeh-Rud Reservoir will decrease by 21 to 38%. The results also showed that the water shortages based on the baseline management scenario (B) will be between 334 and 805 MCM (Million Cubic Meters). These range of values varies between 252 and 787 MCM in the water demand management scenario (D). In general, the water shortage can be reduced in the Zayandeh-Rud River Basin with water demand control, but complete resolution of this problem in this region requires more integrated strategies based on a sustainable development, such as a fundamental change in the cropping pattern, prevention of population growth and industrial development.     

Modeling the impacts of climate change on the thermal and oxygen dynamics of Lake Volta

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic Lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1?m) upward shift of thermocline depth resulted in an 8%–12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change.     

统计降尺度方法及其评价指标比较研究

针对目前气候变化对水资源影响研究中关注的问题,以汉江白河上游为研究对象,比较研究统计降尺度方法及其评价指标。以美国环境预报中心/美国国家大气研究中心全球再分析资料、CGCM3和HadCM3的A2情景为大尺度气候背景资料,应用SSVM和SDSM统计降尺度方法对大尺度气候因子进行尺度降解,得到降水情景序列后作为水文模型的输入,通过模拟径流比较分析统计降尺度方法的优劣。研究结果表明,由不同统计降尺度方法得到的降水作为水文模型输入,模拟径流的结果相差很大;对广泛应用于统计降尺度方法的降水模拟评价指标和径流模拟结果进行比较,发现所采用的降水评价指标侧重于考虑降水的统计分布特征,不能完整地描述降水过程特性。分析认为,径流模拟结果应该作为气候变化对径流影响研究中统计降尺度方法评价的重要参考。     

Spatial Patterns and Temporal Variability of Drought in Western Iran

An analysis of drought in western Iran from 1966 to 2000 is presented using monthly precipitation data observed at 140 gauges uniformly distributed over the area. Drought conditions have been assessed by means of the Standardized Precipitation Index (SPI). To study the long-term drought variability the principal component analysis was applied to the SPI field computed on 12-month time scale. The analysis shows that applying an orthogonal rotation to the first two principal component patterns, two distinct sub-regions having different climatic variability may be identified. Results have been compared to those obtained for the large-scale using re-analysis data suggesting a satisfactory agreement. Furthermore, the extension of the large-scale analysis to a longer period (1948–2007) shows that the spatial patterns and the associated time variability of drought are subjected to noticeable changes. Finally, the relationship between hydrological droughts in the two sub-regions and El Niño Southern Oscillation events has been investigated finding that there is not clear evidence for a link between the two phenomena.     

Analysis and prediction of reference evapotranspiration with climate change in Xiangjiang River Basin,China

Reference evapotranspiration(ET_0) is often used to estimate actual evapotranspiration in water balance studies. In this study, the present and future spatial distributions and temporal trends of ET_0 in the Xiangjiang River Basin(XJRB) in China were analyzed. ET_0 during the period from1961 to 2010 was calculated with historical meteorological data using the FAO Penman-Monteith(FAO P-M) method, while ET_0 during the period from 2011 to 2100 was downscaled from the Coupled Model Intercomparison Project Phase 5(CMIP5) outputs under two emission scenarios, representative concentration pathway 4.5 and representative concentration pathway 8.5(RCP45 and RCP85), using the statistical downscaling model(SDSM). The spatial distribution and temporal trend of ET_0 were interpreted with the inverse distance weighted(IDW)method and Mann-Kendall test method, respectively. Results show that:(1) the mean annual ET_0 of the XJRB is 1 006.3 mm during the period from 1961 to 2010, and the lowest and highest values are found in the northeast and northwest parts due to the high latitude and spatial distribution of climatic factors, respectively;(2) the SDSM performs well in simulating the present ET_0 and can be used to predict the future ET_0 in the XJRB; and(3) CMIP5 predicts upward trends in annual ET_0 under the RCP45 and RCP85 scenarios during the period from 2011 to 2100.Compared with the reference period(1961e1990), ET_0 increases by 9.8%, 12.6%, and 15.6% under the RCP45 scenario and 10.2%, 19.1%, and27.3% under the RCP85 scenario during the periods from 2011 to 2040, from 2041 to 2070, and from 2071 to 2100, respectively. The predicted increasing ET_0 under the RCP85 scenario is greater than that under the RCP45 scenario during the period from 2011 to 2100.     

气候变化和人类活动对洮河输沙量变化的影响分析

根据洮河代表水文站近60年的输沙量资料,分析了洮河输沙量变化规律以及气候变化和人类活动对洮河输沙量变化的影响。结果表明:(1)洮河多年平均输沙量为2 295万t,输沙量从1990年开始呈明显递减并且有继续减少的趋势;(2)洮河各代表站输沙量均发生显著突变,突变年份发生在20世纪80年代末和90年代中上期,输沙量突变后比突变前有明显减少;(3)气候变化和人类活动共同影响下洮河输沙量呈减少趋势。总体上,气候变化对输沙量变化的影响要远小于人类活动的影响,20世纪90年代以前气候变化对输沙量的变化影响起主导作用,90年代以后人类活动的影响起主导作用。     

长江源区河流水温对气候变化的响应

基于长江源区沱沱河流域1977~2015年月平均气温、河流水温同步资料,采用线性趋势分析和小波分析方法,研究了沱沱河5~10月气温与水温的年际变化趋势及周期性特征,并进一步分析了水温与同期气温的线性相关性。结果表明:近40 a来,沱沱河流域5~10月气温和水温均呈现出升温趋势,2011~2015年较1977~1980年气温分别升高0.6,1.3,1.3,1.0,1.3,2.0℃,水温分别升高0.6,1.6,1.7,1.1,1.0,0.2℃;水温上升趋势突变发生时间普遍滞后于气温,突变点分别在1997~2003年和2005~2007年之间;7~10月水温与气温变化均存在明显的28 a时间尺度的主周期,而5,6月气温与水温周期不一致;水温与气温的相关关系密切,可以认为气温变化是影响水温变化的主要原因之一。     

The role of the Pearl River flow in Deep Bay hydrodynamics and potential impacts of flow variation and land reclamation

Deep Bay (DB) is a semi-enclosed bay that opens to the middle part of the Pearl River Estuary (PRE), the largest estuarine wetland area in the world. Like many rivers around the world, the Pearl River has in recent years experienced more frequent and more severe flow variations. It was hypothesized that Pearl River flow variation would affect the environment of DB, where locates large area of Ramsar wetlands of international importance. The anthropogenic factor of land reclamation was also hypothesized to alter the Pearl River flow and thus affect DB and the PRE environment. Simulations were performed to model water and salt transport processes under different scenarios of Pearl River flow variation and land reclamation. It was found that the Pearl River had a strong governing role on the hydrodynamics of DB, especially in the wet season. The simulation results indicated that in the wet season, the waters at the mouth of DB and DB as a whole were respectively composed of 50–80% and 31–37% of water discharged from the Pearl River. Moreover, it was shown that a 20% increase in Pearl River flow in the wet season would result in 0.2% and 3.3% more Pearl River water flushing into the bay before and after reclamation, respectively. Therefore, reclamation is predicted to stress the coastal ecosystem in DB, as it will enhance the intrusion of pollutants from the Pearl River into the bay head. However, it would benefit the removal and dilution of pollutants directly discharged into the bay from the Shenzhen River. Our results confirm that the hydrodynamic interconnection of bay and estuary in an estuarine system is complex, and should be carefully examined when assessing the environmental impacts of climate change and anthropogenic engineering projects.     

Human and climate impacts on Columbia River hydrology and salmonids

The Columbia River had until recently the world's largest Chinook salmon runs. Restoration of the system's severely decimated runs requires understanding changes in the hydrologic variables (e.g. flow and sediment transport) important to salmonids. We describe here methods to distinguish the human and climate‐induced contributions to Columbia River hydrologic processes relevant to the crucial seaward spring migration of juveniles through the tidal river and estuary. Flow regulation has caused most of the decrease in peak flow and sediment transport; it has contributed to changes in spring freshet timing. Climate change has reduced peak and average flows and sediment transport, changing spring‐freshet timing by several weeks. Irrigation diversion has reduced the annual average flow as much as climate change. A better understanding of historical changes in hydrologic processes entailed in this paper tells us how management and climate have changed the Columbia River system over time. The separation of the climate and anthropogenic influences used here may assist in policy analyses and strategies aimed at restoration of the Columbia River endangered salmonids, and in management of other systems. Copyright © 2010 John Wiley & Sons, Ltd.     

气候变化对科尔沁沙地蒸散发和植被的影响

近30年来科尔沁沙地的植被呈现显著退化,揭示气候变化下科尔沁沙地关键生态水文过程(如蒸散发和植被)的变化特征及其影响对荒漠化防治具有重要意义。本研究开发了水文过程与植被生长耦合的生态水文模型(WaVEM),模拟解析了科尔沁沙地各气象因子变化对实际蒸散发和植被变化的影响程度,探讨了气候变化下科尔沁沙地植被变化的响应规律。结果表明,1964—2013年间,在降水变化不显著而气温显著升高情况下,实际蒸散发和年最大叶面积指数均未发生显著变化。降水的年际变化是导致实际蒸散发和植被变化的主要因素,潜在蒸发的影响次之。短期的干旱会导致植被锐减,而短期干旱结束后植被能够迅速恢复;多年连续干旱是导致科尔沁植被显著退化的主要因素。     

Effect of management strategies on reducing negative impacts of climate change on water resources of the Isfahan–Borkhar aquifer using MODFLOW

Recently, many studies have investigated the effect of climate change on groundwater resources in semiarid and arid areas and have shown adverse effects on groundwater recharge and water level. However, only a few studies have shown suitable strategies for reducing these adverse effects. In this study, climate conditions were predicted for the future period of 2020–2044, under the emission scenarios of RCP2.6, RCP4.5, and RCP8.5, for Isfahan–Borkhar aquifer, Isfahan, Iran, using MODFLOW‐2000 (MODFLOW is United States Geological Survey product). Results showed that the average groundwater level of the aquifer would decrease to 13, 15, and 16 m in 2012 to 2044 approximately under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively. Then, three groundwater sustainability management scenarios were defined that included 10%, 30%, and 50% reduction in groundwater extraction. These strategies simulated the reduced negative effects of climate change on the aquifer. The results showed that decreases in water withdrawal rates of 10%, 30%, and 50% under RCP8.5 scenario (critical scenario) could decrease the mean groundwater level by 14, 11, and 7 m, respectively. The main result of the study showed that 50% reduction in groundwater withdrawal may increase the groundwater levels significantly in order to restore the aquifer sustainability in the study area. In this study, with assuming that the current harvest of wells in the future period is constant, so the results of studies showed that for the aquifer's sustainability management, the water abstraction from the aquifer should reduce up to 50% of the existing wells. Changing the irrigation method from surface to subdroplet irrigation plays an important role in reducing the withdrawal from the aquifer. The results of a study in Iran have shown that the change in the irrigation method from surface to subdroplet irrigation causes a 40% reduction in water use for agriculture.     

全球气候变化对中国淡水资源及其脆弱性影响研究综述

由温室效应引发的全球气候变化问题已成为世界各国政府和专家、学者关心的焦点问题。在分析近几十年来我国淡水资源变化特点及气候条件波动或变化对径流现实影响的基础上,较系统地总结了近10年我国在气候变化影响的某些方面的研究成果,主要集中在我国淡水资源对气候变化的敏感性和水资源在气候变化情景下的脆弱性两个方面的问题。     

博尔塔拉河径流过程对气候变化的响应

以博尔塔拉河上游和中游为研究区,利用温泉站、博乐站1992-2012年月径流、降水、温度数据,采用统计分析、Mann-Kendall非参数检验、水文特征分析参数分析了博河流域气候变化对径流的影响,得出以下结论:120世纪90年代以来,博尔塔拉河上游和中游径流量均呈波动上升趋势,其中近10年径流量增加趋势明显。2径流年际变化上游较稳定,而径流年内变化正好相反,且上游径流变化具有水热同期的特点,而中游具有滞后性。3温度是引起上游径流变化的主要因素,而农业灌溉、温度、降水的变化对中游径流变化有重要影响,其中温度的影响最为显著。