Both climate and land use changes can influence water quality and quantity in different ways. Thus, for predicting future water quality and quantity trends, simulations should ideally account for both projected climate and land use changes. In this paper, land use projections and climate change scenarios were integrated with a hydrological model to estimate the relative impact of climate and land use projections on a suite of water quality and quantity endpoints for a Canadian watershed. Climatic time series representing SRES change scenario A2 were generated by downscaling the outputs of the Canadian Regional Climate Model (version 4.1.1) using a combination of quantile-quantile transformation and nearest neighbor search. The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow, nitrogen and phosphorus loading under different climate and land use scenarios. Results showed that a) climate change will drive up maximum monthly streamflow, nitrate loads, and organic phosphorus loads, while decreasing organic nitrogen and nitrite loads; and b) land use changes were found to drive the same water quality/quantity variables in the same direction as climate change, except for organic nitrogen loads, for which the effects of the two stressors had a reverse impact on loading.Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

作为联结大气圈和地圈的纽带,水文循环同时承受气候变化和土地利用/覆被变化（LUCC）的双重影响,然而大多数的水文响应研究主要关注未来气候变化对径流的影响,忽略了未来LUCC的作用。因此,本文的研究目的是评估未来气候变化和LUCC对径流的共同影响。首先采用2种全球气候模式（BCC-CSM1.1和BNU-ESM）输出,基于DBC降尺度模型得到未来气候变化情景;然后,利用CA-Markov模型预测未来LUCC情景;最后,通过设置不同的气候和LUCC情景组合,采用SWAT模型模拟汉江流域的未来径流过程,定量评估气候变化和LUCC对径流的影响。结果表明：① 未来时期汉江流域的年降水量、日最高、最低气温相较于基准期（1966—2005年）,在RCP 4.5和RCP 8.5浓度路径下,分别增加4.0%、1.8 ℃、1.6 ℃和3.7%、2.5 ℃、2.3 ℃;② 2010—2050年间,流域内林地和建设用地的面积占比将分别增加2.8%和1.2%,而耕地和草地面积占比将分别减少1.5%和2.5%;③ 与单一气候变化或LUCC情景相比,气候变化和LUCC共同影响下的径流变化幅度最大,在RCP 4.5和RCP 8.5浓度路径下未来时期年平均径流分别增加5.10%、2.67%,且气候变化对径流的影响显著大于LUCC。本文的研究结果将有助于维护未来气候变化和LUCC共同影响下汉江流域的水资源规划与管理。

As a link between the atmosphere and the geosphere, the hydrological cycle is affected by both climate change and Land Use/Cover Change (LUCC). However, most existing research on runoff response focused mainly on the impact of the projected climate variation, neglecting the influence of future LUCC variability. Therefore, the objective of this study is to examine the co-impacts of both projected climate change and LUCC on runoff generation. Firstly, the future climate scenarios under BCC-CSM1.1 and BNU-ESM are both downscaled and corrected by the Daily Bias Correction (DBC) model. Secondly, the LUCC scenarios are predicted based on the Cellular Automaton-Markov (CA-Markov) model. Finally, the Soil and Water Assessment Tool (SWAT) model is used to simulate the hydrological process under different combinations of climate and LUCC scenarios, with the attempt to quantitatively evaluate the impacts of climate change and LUCC on runoff generation. In this study, the Hanjiang River basin is used as the case study area. The results show that: (1) compared with the base period (1966-2005), the annual rainfall, daily maximum and minimum air temperatures during 2021-2060 will have an increase of 4.0%, 1.8 ℃, 1.6 ℃ in RCP4.5 scenario, respectively, while 3.7%, 2.5 ℃, 2.3 ℃ in RCP8.5 scenario, respectively. (2) During 2010-2050, the area proportions of forest land and construction land in the study area will increase by 2.8% and 1.2%, respectively, while those of farmland and grassland will decrease by 1.5% and 2.5%, respectively. (3) Compared with the single climate change or LUCC scenario, the variation range of future runoff under both climate and LUCC is the largest, and the influence of climate change on future runoff is significantly greater than that of LUCC. This study is helpful to maintain the future water resources planning and management of the Hanjiang River basin under future climate and LUCC scenarios.

热带地区已有大量原始林转变为其他土地利用类型,影响了陆地生态系统的水源涵养功能.为了明确热带原始林转变为其他土地类型对土壤水源涵养功能的影响,在海南中部山区选择4种典型土地利用类型,包括林龄大于100年的原始林(VF)、10年生次生林(SF)、12年生槟榔林(AF)和35年生橡胶林(RF),评估土地利用变化对土壤持水性能和水源涵养功能指数(SWI)的影响.结果表明: 与原始林相比,表层土壤(0～10 cm)中,其他土地类型土壤持水性能指标均降低,12年槟榔林各土层指标均最低.土壤含水量和最大持水量与植被郁闭度、土壤有机质和土壤容重显著相关,表明郁闭度、土壤有机质和紧实度的改变是土壤持水性能变化的重要原因.与原始林相比,次生林、槟榔林和橡胶林土壤水源涵养功能分别减少27.7%、54.3%和11.5%,不同土层的差异各异,橡胶林仅表层土壤水源涵养功能显著降低.植被郁闭度、土壤有机质和土壤容重可解释土壤水源涵养功能变量的83.3%.土地利用转变显著改变了土壤持水性能和土壤水源涵养功能,相比12年槟榔林,35年橡胶林能更好地保持土壤水分,土地管理中增加土壤有机质和减少土壤紧实度可改善土壤持水性能及水源涵养功能.

In tropical areas, a large number of natural forests have been transformed into other plantations, which affected the water conservation function of terrestrial ecosystems. In order to clari-fy the effects of land use changes on soil water conservation function, we selected four typical land use types in the central mountainous region of Hainan Island, <em>i.e.</em>, natural forests with stand age greater than 100 years (VF), secondary forests with stand age of 10 years (SF), areca plantations with stand age of 12 years (AF) and rubber plantations with stand age of 35 years (RF). The effects of land use change on soil water holding capacity and water conservation (presented by soil water index, SWI) were assessed. The results showed that, compared with VF, the soil water holding capacity index of other land types decreased in the top soil layer (0-10 cm). AF had the lowest soil water holding capacity in all soil layers. Soil water content and maximum water holding capacity were significantly related to canopy density, soil organic matter and soil bulk density, which indicated that canopy density, soil organic matter and compactness were important factors influencing soil water holding capacity. Compared to VF, soil water conservation of SF, AF and RF were reduced by 27.7%, 54.3% and 11.5%, respectively. The change of soil water conservation was inconsistent in different soil layers. Vegetation canopy density, soil organic matter and soil bulk density explained 83.3% of the variance of soil water conservation. It was suggested that land use conversion had significantly altered soil water holding capacity and water conservation function. RF could keep the soil water better than AF in the research area. Increasing soil organic matter and reducing soil compaction would be helpful to improve soil water holding capacity and water conservation function in land management.

土地利用/覆被变化是导致流域水资源发生变化的重要原因.以中国西北地区的洮河流域为研究区,构建适宜于洮河流域的分布式水文模型(SWAT),在综合考虑流域1985-2000年间土地利用/覆被变化特征的基础上建立多种土地利用/覆被情景,并对不同情景下的水文过程进行模拟,得到以下结论:(1)经校准后的SWAT模型,其验证期的相关系数R²、相对误差R_e和效率系数E_ns分别为0.83、-8%和0.68,说明SWAT模型在洮河流域径流量模拟中具有较高的适用性.(2)草地、林地和耕地是洮河流域的主要土地利用类型.林地的壤中流、土壤湿度和产水量最大,耕地的地表径流和蒸散量最大.与1985年相比,2000年土地利用/覆被情景下地表径流增加了1.72%,地下径流和产水量降低了0.8%和0.4%;耕地扩张和城镇建设用地情景下流域地表径流明显增加,生态恢复情景下流域地表径流和产水量均有所降低.(3)从月径流量来看,林草地可以减小最大与最小流量的变幅,而耕地的作用正好相反.与1985年相比,2000年土地利用/覆被情景下汛期地表径流增加1.67%,地下径流减少0.83%,产水量减少0.36%;非汛期地表径流增加1.86%,地下径流减少0.63%,产水量减少0.46%.说明林草地减少对非汛期的影响更大.

Land-use/cover change is the important reason for water resource changing in a basin. The Taohe River basin in Northwest China is studied with the distributed hydrological model SWAT (Soil and Water Assessment Tool). Land-use/cover scenarios are constructed based on comprehensive consideration of the variation characteristics of the land-use/cover change from 1985 to 2000. Then the hydrological processes are simulated and the hydrological response in different scenarios at basin scale are discussed. The results show that: (1) After successful calibration verification, the correlation coefficient (<i>R</i>²), relative error (<i>R</i>_e) and Nash-Suttcliffe coefficient (<i>E</i>_ns) of SWAT model are 0.83, -8% and 0.68, respectively. It is demonstrated that the calibrated SWAT model can well simulate the monthly runoff, and is thus applicable to study the Taohe River basin. (2) The main types of land-use/cover in Taohe River basin are pasture, forest and farmland. When the interflow, soil moisture and water yield in forest land reach the maximum, runoff and evapotranspiration of farmland reach the maximum. As compared with the land-use/cover scenarios in 1985, under the land-use/cover scenarios in 2000 the annual runoff increased 1.72%, but the underground runoff and water yield decreased by 0.8% and 0.4%, respectively. The annual runoff of farmland expansion scenario and urban expansion scenario significantly increased surface runoff, but the annual runoff and water yield decreased under ecological restoration scenario. (3) The forest and grassland can reduce the amplitude of monthly runoff between maximum and minimum, while farmland shows an opposite result. As compare with the land-use/cover in 1985, the land-use/cover in 2000 scenario shows that the runoff increased by 1.67%, while underground runoff and water yield decreased by 0.83% and 0.36% in flood season; in non-flood season the surface runoff increased by 1.86%, while underground runoff and water yield decreased by 0.63% and 0.46%. The results demonstrate that forest and grassland area reduction has more influence on hydrologic cycle in non-flood season.

选用国内外广泛应用的SWAT分布式水文模型，定量分析流溪河流域土地利用与气候变化对径流的影响，采用情景模拟分析方法设置3类情景进行定量分析.对上中下游的温泉、太平场和南岗3个水文站依次校正与验证得出：除温泉站在验证期的3个系数刚达标之外，其他的相对误差＜15%、相关系数＞0.8、NashSutcliffe效率系数＞0.75，说明SWAT模型在流溪河流域的径流量模拟中具有较高的适用性.综合型情景模拟分析得出：以1991&mdash;2000年为基准期，2001&mdash;2010年土地利用与气候变化综合引起年均径流量增加11.23 m³&middot;s^-1，土地利用变化引起年均径流量减少0.62 m³&middot;s^-1，气候变化引起年均径流量增加11.85 m³&middot;s^-1，气候变化的影响强度强于土地利用变化的影响强度.极端土地利用情景模拟分析得出：与2000年土地利用现状模拟径流量相比，耕地情景和草地情景的径流量分别增加2.7%和0.5%，林地情景的径流量减少0.7%，证明林地有一定的截流能力.气候变化情景模拟分析得出：流域径流量变化与降水变化呈正相关关系（降水每升高10%，径流平均增加11.6%），与气温变化呈负相关关系（气温每升高1 ℃，径流平均降低0.8%），降水变化的影响强度强于气温变化的影响强度.在气候变化环境下，需要重视对强降雨的预测和灾害预防，可通过优化土地利用结构与空间布局来减缓气候变化带来的水文负效应，如洪涝灾害.

SWAT model, an extensively used distributed hydrological model, was used to quantitatively analyze the influences of changes in land use and climate on the runoff at watershed scale. Liuxihe Watershed' s SWAT model was established and three scenarios were set. The calibration and validation at three hydrological stations of Wenquan, Taipingchang and Nangang showed that the three factors of Wenquan station just only reached the standard in validated period, and the other two stations had relative error (RE) < 15%, correlation coefficient (R2) > 0.8 and Nash-Sutcliffe efficiency valve (Ens) > 0.75, suggesting that SWAT model was appropriate for simulating runoff response to land use change and climate variability in Liuxihe watershed. According to the integrated scenario simulation, the annual runoff increased by 11.23 m3 x s(-1) from 2001 to 2010 compared with the baseline period from 1991 to 2000, among which, the land use change caused an annual runoff reduction of 0.62 m3 x s(-1), whereas climate variability caused an annual runoff increase of 11.85 m3 x s(-1). Apparently, the impact of climate variability was stronger than that of land use change. On the other hand, the scenario simulation of extreme land use showed that compared with the land use in 2000, the annual runoff of the farmland scenario and the grassland scenario increased by 2.7% and 0.5% respectively, while that of the forest land scenario were reduced by 0.7%, which suggested that forest land had an ability of diversion closure. Furthermore, the scenario simulation of climatic variability indicated that the change of river runoff correlated positively with precipitation change (increase of 11.6% in annual runoff with increase of 10% in annual precipitation), but negatively with air temperature change (reduction of 0.8% in annual runoff with increase of 1 degrees C in annual mean air temperature), which showed that the impact of precipitation variability was stronger than that of air temperature change. Therefore, in face of climate variability, we need to pay attention to strong rainfall forecasts, optimization of land use structure and spatial distribution, which could reduce the negative hydrological effects (such as floods) induced by climate change.

Along with rapid economic development and population growth, anthropogenic disturbances to natural ecosystems increase the progressively worsening environmental problems in and around water resources, making the potential ecological risks more severe and unpredictable. In order to cope with the increasingly serious issues related to the ecological environment and poverty alleviation, the Government of Yunnan in Southwest China launched a large-scale afforestation campaign (plantation forestry) on the Yunnan-Guizhou Plateau, which is the main source of several major river systems in Southeast Asia. In this study, we use GIS to investigate the impacts of a large-scale afforestation on the water storage balance of Southeast Asia. Results show an expansion of the arid zone in the Yunnan-Guizhou Plateau in recent years, and runoff from rivers has decreased year after year. In contrast to natural forests, planted forests are a characteristic of more water shortages, less rainfall, and higher evapotranspiration rates. Moreover, planted forests may exacerbate conflicts between humans and nature over water resources. Additionally, with respect to downstream populations affected by the government's afforestation policy, China has bore the brunt of the resultant water scarcity predicament (approximately 52.29%), followed by Vietnam (26.39%), Laos (6.78%), Cambodia (6.16%), Thailand (4.42%), and Myanmar (3.96%). To alleviate this problem and the potential crises that may result from it, the Government of China should change its policy from its focus on afforestation to promoting natural vegetation conservation practices.

土地利用和气候变化是流域水资源发生变化的重要原因。以洮河流域为研究区，通过模型率定得到适宜于洮河流域的分布式水文模型（SWAT），在综合考虑流域土地利用和气候变化特征的基础上构建多种情景模式，并对不同情景模式下的水文特征进行模拟，得到以下结论：（1）校准后的SWAT模型，R²、R_e和E_ns分别达到0.83、-8%和0.68，说明该模型在洮河流域径流模拟中具有较好的适用性。（2）与1976-1995年相比，气候变化使流域产水量增加1.30 mm，土地利用变化使流域产水量减少0.77 mm。土地利用变化对水文特征的影响小于气候变化，但土地利用变化对流域管理的作用却是不可忽视的。从极端土地利用变化情景可知，与1985年土地利用情景相比，林地、草地和耕地情景中产水量分别变化了18.1%、-7.4%和-10.1%。从气候变化情景可知，当降水量不变，温度分别变化2 ℃、1 ℃、-1 ℃和-2 ℃时，流域产水量的变化量分别为-4.23%、-2.56%、3.08%和6.70%；当温度不变，降水量分别变化20%、10%、-10%和-20%时，流域产水量的变化量分别为56.32%、30.88%、-23.66%和-45.94%。（3）在土地利用和气候变化共同作用下，地表径流增加的区域主要位于下游的广河县、和政县和康乐县以及上游的碌曲县和夏河县等地，地表径流增加地区的面积约占流域总面积的39%。