Abstract
Land use change and climate variability are two key factors impacting watershed hydrology, which is strongly related to the availability of water resources and the sustainability of local ecosystems. This study assessed separate and combined hydrological impacts of land use change and climate variability in the headwater region of a typical arid inland river basin, known as the Heihe River Basin, northwest China, in the recent past (1995–2014) and near future (2015–2024), by combining two land use models (i.e., Markov chain model and Dyna-CLUE) with a hydrological model (i.e., SWAT). The potential impacts in the near future were explored using projected land use patterns and hypothetical climate scenarios established on the basis of analyzing long-term climatic observations. Land use changes in the recent past are dominated by the expansion of grassland and a decrease in farmland; meanwhile the climate develops with a wetting and warming trend. Land use changes in this period induce slight reductions in surface runoff, groundwater discharge and streamflow whereas climate changes produce pronounced increases in them. The joint hydrological impacts are similar to those solely induced by climate changes. Spatially, both the effects of land use change and climate variability vary with the sub-basin. The influences of land use changes are more identifiable in some sub-basins, compared with the basin-wide impacts. In the near future, climate changes tend to affect the hydrological regimes much more prominently than land use changes, leading to significant increases in all hydrological components. Nevertheless, the role of land use change should not be overlooked, especially if the climate becomes drier in the future, as in this case it may magnify the hydrological responses.
Highlights
It is widely agreed that land use change and climate variability are two active environmental factors profoundly affecting watershed hydrology [1,2,3]
By taking advantage of an integrated modeling approach which combines the Markov chain, Dyna-CLUE and SWAT models, we aim to address the following questions: (i) how has the land use and climate changed in the recent past from 1995 to 2014? (ii) what are their roles in affecting hydrological regimes? and (iii) how may the hydrological conditions be impacted by land use change and/or climate variability in the near future, from 2015 to 2024, given different scenarios?
The results show that the joint effects lead to consistent growths in surface runoff, groundwater discharge, ET and streamflow by 18.29%, 11.53%, 9.47% and 11.96%, respectively, which are highly similar to those solely induced by climate changes
Summary
It is widely agreed that land use change and climate variability are two active environmental factors profoundly affecting watershed hydrology [1,2,3]. Climate variability brings distinct changes to hydrological regimes and influences spatial and temporal patterns of water resources in a region [5]. It was reported in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [6] that a warming climate in the past half century has occurred in almost every region across the world, especially in the midlatitudes of the northern hemisphere [7]. There is no a clear trend in precipitation since 1960 and future projections are subject to high uncertainty [8] The changes in both temperature and precipitation exhibit remarkable regional variability; the northwest China is projected to experience a warmer and wetter climate in the future [10]. The rising temperature accompanied with altered precipitation patterns and intensity may have substantial hydrological consequences such as accelerating the hydrological cycle and increasing the frequency of occurrence of hydrological extremes, in the arid regions of northwest China where the scarcity of water resources heavily constrains the local agricultural and economic developments [11,12,13]
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