Impacts of forestation on the annual and seasonal water balance of a tropical catchment under climate change

Background:This study aims to assess the effects of a forestation program and climate change on the annual and seasonal water balance of the Bogowonto catchment(597 km^(2))in Java,Indonesia.The catchment study is rare example in Indonesia where forestation has been applied at the catchment level.However,since the forestation program has been initiated,evaluations of the program only focus on the planting area targets,while the environmental success e.g.,impacts on the hydrological processes have never been assessed.This study used a calibrated Soil and Water Assessment Tool(SWAT)model to diagnose the isolated and combined effects of forestation and climate change on five water balance components,namely streamflow(Q),evapotranspiration(ET),surface runoff(Q_(s)),lateral flow(Q_(l))and base flow(Q_(b)).Results:The results show that from 2006 to 2019,forest cover has increased from 2.7% to 12.8% of the total area,while in the same period there was an increase in the mean annual and seasonal temperature,rainfall,and streamflow.Results of SWAT simulations show that changes in the mean annual and seasonal water balance under the forestation only scenario were relatively minor,while changes were more pronounced under the climate change only scenario.Based on the combined impacts scenario,it was observed that the effects of a larger forest area on the water balance were smaller than the effects of climate change.Conclusions:Although we found that forestation program has minor impacts compared to that of climate change on the hydrological processes in the Bogowonto catchment,seasonally,forestation activity has decreased the streamflow and surface runoff during the wet season which may reduce the risk of moderate floods.However,much attention should be paid to the way how forestation may result in severe drought events during the dry season.Finally,we urge the importance of accounting for the positive and negative effects in future forestation programs.

The Impacts of Climate Change on the Availability of Surface Water Resources in Jordan

Climate change in the Middle East area including Jordan has started to be reflected in decreasing precipitation and increasing temperatures with their impacts on the availability of surface and groundwater. This article aims to evaluate the impacts of decreasing or increasing precipitation by 10% and 20% on the quantities of flood runoff based on recorded precipitation and runoffs of catchments during the past 60 to 70 years of observation, during which the precipitation in individual or a few years increased or decreased by tens of percentages relative to the long-term average precipitation. The results of quantification show that in Jordan as a whole, decreasing precipitation by 10% and 20% has historically (during the recording period) resulted in reductions in flood flows by 26.2% and 52.8% and that increasing precipitation by 10% and 20% has resulted in increases in flood flows by 26.4% and 56.5% respectively. These results look somehow paradox, because the general perception is that flood runoff changes in the same percentage like precipitation although flood flow is not linearly correlated with precipitation but exponentially. Decreasing precipitation in the water-scarce stressed country, Jordan due to climatic changes, will have strong implications on rain-fed and irrigated agriculture and on household water supplies with very severe socio-economic percussions expressed in increasing unemployment and poverty which may lead to social and political unrest. Therefore, proactive measures have to be implemented before disasters hit. Such measures are limited in Jordan to seawater desalination, intensified water harvesting and improved water use efficiency in agriculture.

Implementation of a Surface Runoff Model with Horton and Dunne Mechanisms into the Regional Climate Model RegCM_NCC

A surface runoff parameterization scheme that dynamically represents both Horton and Dunne runoff generation mechanisms within a model grid cell together with a consideration of the subgrid-scaie soil heterogeneity, is implemented into the National Climate Center regional climate model （RegCM_NCC）. The effects of the modified surface runoff scheme on RegCMANCC performance are tested with an abnormal heavy rainfall process which occurred in summer 1998. Simulated results show that the model with the original surface runoff scheme （noted as CTL） basically captures the spatial pattern of precipitation, circulation and land surface variables, but generally overestimates rainfall compared to observations. The model with the new surface runoff scheme （noted as NRM） reasonably reproduces the distribution pattern of various variables and effectively diminishes the excessive precipitation in the CTL. The processes involved in the improvement of NRM-simulated rainfall may be as follows： with the new surface runoff scheme, simulated surface runoff is larger, soil moisture and evaporation （latent heat flux） are decreased, the available water into the atmosphere is decreased; correspondingly, the atmosphere is drier and rainfall is decreased through various processes. Therefore, the implementation of the new runoff scheme into the RegCMANCC has a significant effect on results at not only the land surface, but also the overlying atmosphere.

Modelling Hydrological Consequences of Climate Change—Progress and Challenges

The simulation of hydrological consequences of climate change has received increasing attention from the hydrology and land-surface modelling communities. There have been many studies of climate-change effects on hydrology and water resources which usually consist of three steps： （1） use of general circulation models （GCMs） to provide future global climate scenarios under the effect of increasing greenhouse gases, （2） use of downscaling techniques （both nested regional climate models, RCMs, and statistical methods） for ＂downscaling＂ the GCM output to the scales compatible with hydrological models, and （3） use of hydrologic models to simulate the effects of climate change on hydrological regimes at various scales. Great progress has been achieved in all three steps during the past few years, however, large uncertainties still exist in every stage of such study. This paper first reviews the present achievements in this field and then discusses the challenges for future studies of the hydrological impacts of climate change.

Modeling the Impact of Climate Change in A Mediterranean Catchment(Merguellil,Tunisia)

Climate change impact studies on hydrologic regime have been until recently restricted mainly because of the coarse spatial and temporal resolution of the Global Circulation Models(GCMs)outputs. Nevertheless,local meteorological variables can be derived from GCMs scenarios using downscaling techniques.In the present study,the Statistical DownScaling Model(SDSM)was selected for

Impact on Water Resources in a Mountainous Basin under the Climate Change Transient Scenario (UKTR)

The impact of climate change on the hydrological regime and water resources in the basin of Venetikos river, in Greece is assessed. A monthly conceptual water balance model was calibrated in this basin using historical hydro meteorological data. This calibrated model was used to estimate runoff under a transient scenario (UKTR) referring to year 2080. The results show that the mean annual runoff, mean winter and summer runoff values, annual maximum and minimum values, as well as, monthly maximum and minimum, will be reduced. Additionally, an increase of potential and actual evapotranspiration was noticed due to temperature increase.

Response of runoff to climate change and its future tendency in the source region of Yellow River

This study examines the hydrological and meteorological data of the source region of the Yellow River from 1956 to 2010 and future climate scenarios from regional climate model （PRECIS） during 2010-2020. Through analyzing the flow variations and revealing the climate causes, it predicts the variation trend for future flows. It is found that the annual mean flow showed a decreasing trend in recent 50 years in the source region of the Yellow River with quasi-periods of 5a, 8a, 15a, 22a and 42a; the weakened South China Sea summer monsoon induced precipitation decrease, as well as evaporation increase and frozen soil degeneration in the scenario of global warming are the climate factors, which have caused flow decrease. Based on the regional climate model PRECIS prediction, the flows in the source region of the Yellow River are likely to decrease generally in the next 20 years.

Response of water resources to climate change and its future trend in the source region of the Yangtze River

In this paper, variations of surface water flow and its climatic causes in China are analyzed using hydrological and meteorological observational data, as well as the impact data set （version 2.0） published by the National Climate Center in November 2009. The results indicate that surface water resources showed an increasing trend in the source region of the Yangtze River over the past 51 years, especially after 2004. The trend was very clearly shown, and there were quasi-periods of 9 years and 22 years, where the Tibetan Plateau heating field enhanced the effect, and the plateau monsoon entered a strong period. Precipitation notably increased, and glacier melt water increased due to climate change, all of which are the main climatic causes for increases in water resources in the source region. Based on global climate model prediction, in the SRESA1B climate change scenarios, water resources are likely to increase in this region for the next 20 years.

EVALUATING THE WATER RESOURCE IMPACTS OF CLIMATIC WARMING IN COLD ALPINE REGIONS BY THE WATER BALANCE MODEL: MODELING THE URUMQI RIVER BASIN

In view of the tendency of global climatic warming, the water balance model is employed to estimate the runoff changes in the Urumqi River Basin, Xinjiang Region, China, under ten climate change scenarios, which are combinations of temperature increases by 2K and 4K with precipitation change of 0, ±10% and ±20%, respectively, as the atmospheric concentration of carbon dioxide increases. The results suggest that runoff changes mainly depend on the precipitation change in the glacier-free or less glacierized basins in cold alpine regions. Effect of temperature on runoff becomes marked gradually with the increase in precipitation. Runoff from glacierized areas, however, is much more sensitive to the temperature change.

Hydrological characteristics and changes in the Nu-Salween River basin revealed with model-based reconstructed data

The Nu-Salween River(NSR),the longest free-flow river in Southeast Asia,plays an irreplaceable role in social development and ecological protection.The lower NSR region is particularly valuable as it is inhabited by approximately 6.7 million people.The basin has limited hydraulic conservancy infrastructure and insufficient ability to cope with climate change risks.Studying the hydrological characteristics and changes in the basin provides the scientific basis for rational protection and development of the basin.However,owing to the limitation of observation data,previous studies have focused on the local area and neglected the study of the lower reaches,which is not enough to reflect the spatial characteristics of the entire basin.In this study,the ECMWF 5th generation reanalysis data(ERA5)and Multi-Source Weighted-Ensemble Precipitation(MSWEP)were applied to develop a geomorphology-based hydrological model(GBHM)for reconstructing hydrological datasets(i.e.GBHM-ERA5 and GBHM-MSWEP).The reconstructed datasets covering the complete basin were verified against the gauge observation and compared with other commonly used streamflow products,including Global Flood Awareness System v2.1,GloFAS-Reanalysis dataset v3.0,and linear optimal runoff aggregate(LORA).The comparison results revealed that GBHM-ERA5 is significantly better than the other four datasets and provides a good reproduction of the hydrological characteristics and trends of the NSR.Detailed analysis of GBHM-ERA5 revealed that:(1)A multi-year mean surface runoff represented 39%of precipitation over the basin during 1980–2018,which had low surface runoff in the upstream,while areas around the Three Parallel Rivers Area and the estuary had abundant surface runoff.(2)The surface runoff and discharge coefficient of variations in spring were larger than those in other seasons,and the inter-annual variation in the downstream was smaller than that in the upstream and midstream regions.(3)More than 70%of the basin areas showed a decreasing trend in the surface runoff,except for parts of Nagqu,south of Shan State in Myanmar,and Thailand,where surface runoff has an increasing trend.(4)The downstream discharge has dropped significantly at a rate of approximately 680 million cubic metresper year,and the decline rate is greater than that of upstream and midstream,especially in summer.This study provides a data basis for subsequent studies in the NSR basin and further elucidates the impact of climate change on the basin,which is beneficial to river planning and promotes international cooperation on the water-and eco-security of the basin.

Hydrologic modeling of the Heihe watershed by DLBRM in Northwest China

Water shortage is a chronic problem in arid Northwest China.The rapid population growth and expanding urbanization as well as potential climate change impacts are likely to worsen the situation,threatening domestic,irrigation,and industrial supplies and even the survival of the ecosystems in Northwest China.This paper describes the preliminary work of adapting the Distributed Large Basin Runoff Model(DLBRM) to the Heihe watershed(the second largest inland river in arid Northwestern China,with a drainage area of 128,000 km2) for understanding distribution of glacial-snow melt,groundwater,surface runoff,and evapotranspi-ration,and for assessing hydrological impacts of climate change and glacial recession on water supply in the middle and lower reaches of the watershed.Preliminary simulation results show that the Qilian Mountain in the upper reach area produces most runoff in the Heihe watershed.The simulated daily river flows during the period of 1990-2000 indicate that the Heihe River dis-charges about 1×109 m3 of water from the middle reach(at Zhengyixia Station) to lower reach,with surface runoff and interflow contributing 51 and 49 percent respectively.The sandy lower soil zone in the middle reach has the highest evapotranspiration rate and also contributes nearly half of the river flow.Work underway focuses on the DLBRM model improvement and incorporation of the climate change and management scenarios to the hydrological simulations in the watershed.

基于区域水平衡理论和SWAT模型的沁河流域水收支平衡演变分析

基于区域水平衡理论和SWAT模型,提出了分布式水收支平衡模型的构建思路及水收支平衡计算方法,对人类活动和未来气候变化情景下的沁河流域水收支平衡状况进行模拟,并通过皮尔逊相关系数和Mann-Kendall检验方法分析了水收支平衡的关键影响要素及其演变规律。结果表明:2010—2016年沁河流域蓄水总量呈下降趋势,降水量及出口径流量为沁河流域水收支平衡相对关键的影响要素;未来多气候情景下蓄水总量呈上升趋势,多年平均降水量及出口径流量两个关键影响要素的总体变化情况与辐射强迫水平呈正相关关系;典型气候情景SSP2-4.5下降水量及出口径流量在2037—2041年、2061—2063年可能存在突变。

气候变化对南方典型小水电站入库径流及发电的影响

在全球气候变化不断加剧的背景下,降水、气温、蒸发等气象要素的变化对流域水文和水力发电产生重要影响;中国作为水能资源丰富的国家,水力发电在能源结构中具有重要地位,研究气候变化对入库径流和水力发电的影响,对实现水资源和水电能源的可持续开发利用具有重要意义。以位于北江支流的官溪水电站为研究对象,基于19个CMIP6全球气候模式数据,利用RCCC-WBM模型分析了未来气候变化对官溪水电站入库径流和发电量的影响。结果表明:(1)在SSP2-4.5情景下,官溪水电站以上流域的气温、降水均呈现上升趋势;(2)尽管不同GCMs模式预估结果存在一定差异,从19个模式集合平均结果看,官溪水电站未来入库径流和水力发电量将有所增加;(3)与基准期(1981—2020年)相比,2031—2060年和2061—2090年官溪水电站入库流量将增加3.55%[−34.14%,39.84%]和5.66%[−32.27%,41.96%],发电量将可能增加5.87%[−29.3%,50.1%]和8.03%[−27.3%,52.4%]。未来径流和发电潜能的增加为官溪水电站的扩容改造提供了一定的科学依据。

黑白河流域湿地水文蓄调功能量化及对比研究

【目的】位于若尔盖高原的黑河和白河同属黄河上游一级支流,在高寒湿地水文对比研究方面颇具代表性。【方法】按水量平衡原理,采用SWAT模型对黑河和白河流域山地系统出流进行模拟,以此作为平原区湿地的横向补给量;结合降水和蒸散发等垂向水文动态,就两河流域湿地水文过程进行分析;再根据湿地土壤水文物理属性估算其静储量;上述动、静储量相结合,就两河流域湿地水文蓄调的年际变化及其功能进行综合研究。【结果】结果显示:2001—2015年间,黑河流域湿地蓄水累计增持19.48亿m^(3);白河流域湿地蓄水累计减持23.08亿m^(3);黑白河流域湿地静储量分别为20.06亿m^(3)和4.59亿m^(3),泥炭沼泽土静储量最大,永冻土静储量最小;统计期间,湿地蓄调功能指数在黑、白河流域均呈降低趋势,黑河湿地的指数降幅高于白河。【结论】结果表明:SWAT模型在黑、白河流域的适用性良好;研究时段内,黑河流域湿地蓄水总体呈增加状态,白河流域湿地蓄水总体呈减少状态;湿地土壤类型和面积大小是影响静储量的关键因素;黑、白河流域湿地蓄持功能总体发生蜕减。研究可为高寒湿地水文蓄调能力提升暨湿地保护提供方法和数据参考。

气候变化对HBV水文模型参数敏感性和不确定性的影响

阐明气候变化对流域水文模型参数的影响是分析参数可移植性、预估未来水量平衡组分的基础科学问题。基于CMIP6框架下3种数据来源(CNRM、IPSL和MRI)的气象信息,驱动HBV水文模型模拟赣江流域2015—2100年的月径流变化,量化并评估气候变化下控制径流模拟过程典型参数的敏感性和不确定性。研究结果表明:①未来降水增多或减少比持平情况下模型参数敏感性整体更高,其中土壤模块(计算土壤蒸散发和含水量)参数敏感性最高;②区分年内丰枯期与全年平均结果相比,响应模块(划分各径流组分)参数敏感性更高、未来增幅更大,且未来降水增多或减少均会使枯水期土壤模块和响应模块参数的敏感性增高,表明降水量及其年内分配会影响模型参数敏感性;③随机扰动响应模块参数导致的径流不确定性最大(贡献超50%),特别是未来降水增多情景下(超70%),因此,若未来气候变化使径流组分(快速、慢速流比例)大幅变化,需重点关注该模块参数。

天山南坡阿克苏流域冰川物质平衡及其融水径流对气候变化的响应研究

冰川融水是西北干旱区水资源重要组成部分,定量评估其变化对中、下游生态环境保护和工农业经济可持续发展具有重要意义。本文基于国家气象台站日降水和气温资料、数字高程模型(DEM)以及第一次冰川编目数据,利用度日模型模拟了天山南坡阿克苏流域1957—2017年冰川物质平衡及其融水径流变化,分析了融水径流组成及其对气候变化的响应。结果表明:1957—2017年流域年平均物质平衡为-94.6 mm w.e.,61年累积物质平衡为-5.8 m w.e.。流域冰川物质平衡线呈显著上升趋势,年均上升速率为1.6 m/a。研究区年均融水径流量为53.1×10^(8)m^(3),融水增加速率为0.24×10^(8)m^(3)/a,融水径流及其组成分量均呈显著增加趋势。在气候暖湿化背景下,流域降水的增加使得冰川区积累量增加,在剧烈的升温作用下,冰川消融加剧,气温对融水径流的作用增大,因此冰川物质平衡亏损产生的水文效应增强。研究结果可提升区域冰川水资源效应变化及其影响的认识。

基于下垫面变化的月径流模型在滦河中游武烈河、柳河典型子流域的应用

随着气候变化与人类活动的推进,研究基于下垫面变化的月径流模型尤为重要。在对当前主流月径流模型进行总结评估的基础上,结合模型应用过程中所反映的实际问题,对所涉及的关键技术进行了深入研究、改进和整合,并结合研究区水文特性,建立了一个能够综合考虑下垫面变化的月径流水文模型。实例应用表明,模型具有定量识别下垫面变化过程的能力,采用10年分段方法进行下垫面变化过程的识别是可行的,有利于消除水文过程的随机性及模型误差带来的波动性;模型在水资源评价方面可以较方便地进行还原或还现处理,定量分析出下垫面变化对水资源的影响。研究结果对于深入了解流域下垫面变化条件下的径流变化规律及未来不同气候情景下径流效应具有重要的理论意义和现实价值。

黑河中游正义峡径流变化趋势及归因分析

以黑河中游正义峡水文站的实测径流量数据为基础,采用线性回归法、Mann-Kendall突变检验法、滑动t检验法、Pettitt检验法和累积距平法分析了正义峡水文站1970―2020年径流序列的变化趋势和突变年份,并利用基于Budyko假设的水热耦合平衡方程,对正义峡径流量变化趋势进行了归因分析。结果表明:(1)研究期内正义峡径流量波动变化,丰枯交替,但整体呈现增加趋势,2004年径流发生突变,突变后的年平均径流量增加了3.08×10^(8)m^(3),增加率为32.7%。(2)突变后的2005―2020年,正义峡径流量对降水、潜在蒸发和下垫面参数的弹性系数分别为1.40、-0.40、-1.57,且各因子对径流的贡献率分别为42.73%、-12.52%、69.79%,表明径流量对下垫面变化最为敏感,气候因子中降水对径流的影响大于潜在蒸发。(3)在一定的区域气候条件下,植被覆盖、土地利用、流域调水等人类活动引起的中游下垫面变化是正义峡径流量变化的主要原因。研究结果可为流域管理部门制定水资源合理分配及调用方案提供科学依据。

基于SSP情景的黄河源区未来径流模拟预估

受全球气候变化影响,黄河源区的水文情势发生了较大改变,预估气候变化情景下未来流域径流变化趋势对区域水资源利用具有重要意义。利用气候模式数据驱动长短期记忆网络(LSTM)模型,研究了未来近期(2030—2059年)和未来远期(2060—2099年)不同气候变化情景下黄河源区降水和气温的变化趋势,预估了相应径流过程的系统性变化趋势,并采用气候弹性系数法定量分析了气候变化对区域水资源的影响。结果表明:①LSTM模型在黄河源区径流模拟中具有良好的适用性,修正后的模型在训练期和验证期的纳什效率系数分别达到0.84和0.87。②2030—2099年黄河源区的气温呈持续升高态势,年均降水量呈轻微增长趋势,其中汛期降水量减少,非汛期降水量增加。③未来研究区年均径流量呈轻微减少趋势,其中非汛期径流量呈增长趋势,增长幅度大多在30%左右;汛期径流量呈减少趋势,减少幅度为30%~40%。④黄河源区水资源对降水和气温的弹性系数分别为0.392和-0.085,水资源量对降水变化的敏感性高于对气温变化的敏感性。预计降水量变化-15%~25%时,水资源量变化-5.87%~9.79%;气温升高1.0~3.0℃时,水资源量变化-7.29%~-2.42%。

变化环境下青藏高原陆地水储量演变格局及归因

基于1981—2015年全球陆面数据同化系统GLDAS和归一化植被指数GIMMS NDVI3g等多源数据,采用Theil-Sen Median斜率估计和Mann-Kendall趋势检验法探究青藏高原多年陆地水储量(TWS)及其各组分时空演变特征,采用水量平衡法、相关分析法和Hurst指数法识别水循环过程对TWS变化的影响机制。结果表明:受气候变化影响,1981—2015年青藏高原降水及冰川积雪消融增加,TWS以0.7 mm/a的速率增加,青藏高原北部TWS增加趋势极其显著,南部呈减少特征;青藏高原绝大部分地区TWS以0~200 cm的土壤含水量为主,不同深度土壤含水量具有显著空间异质性;青藏高原北部及东部降水主要通过蒸散发过程损失,南部地区径流系数较大。