Modeling large-scale human alteration of land surface hydrology and climate

Yadu N. Pokhrel,Sanghoon Shin,Yusuke Satoh,Tomohito J. Yamada,Farshid Felfelani

doi:10.1186/s40562-017-0076-5

Abstract

Rapidly expanding human activities have profoundly affected various biophysical and biogeochemical processes of the Earth system over a broad range of scales, and freshwater systems are now amongst the most extensively altered ecosystems. In this study, we examine the human-induced changes in land surface water and energy balances and the associated climate impacts using a coupled hydrological–climate model framework which also simulates the impacts of human activities on the water cycle. We present three sets of analyses using the results from two model versions—one with and the other without considering human activities; both versions are run in offline and coupled mode resulting in a series of four experiments in total. First, we examine climate and human-induced changes in regional water balance focusing on the widely debated issue of the desiccation of the Aral Sea in central Asia. Then, we discuss the changes in surface temperature as a result of changes in land surface energy balance due to irrigation over global and regional scales. Finally, we examine the global and regional climate impacts of increased atmospheric water vapor content due to irrigation. Results indicate that the direct anthropogenic alteration of river flow in the Aral Sea basin resulted in the loss of ~510 km3 of water during the latter half of the twentieth century which explains about half of the total loss of water from the sea. Results of irrigation-induced changes in surface energy balance suggest a significant surface cooling of up to 3.3 K over 1° grids in highly irrigated areas but a negligible change in land surface temperature when averaged over sufficiently large global regions. Results from the coupled model indicate a substantial change in 2 m air temperature and outgoing longwave radiation due to irrigation, highlighting the non-local (regional and global) implications of irrigation. These results provide important insights on the direct human alteration of land surface water and energy balances, highlighting the need to incorporate human activities such as irrigation into the framework of global climate models and Earth system models for better prediction of future changes under increasing human influence and continuing global climate change.

Highlights

Expanding human activities have profoundly affected various biophysical and biogeochemical processes of the Earth system over a broad range of scales, and freshwater systems are amongst the most extensively altered ecosystems (Postel et al 1996; Vitousek et al 1997; Nilsson et al 2005; Carpenter et al 2011)
We use the results from a coupled hydrological–climate model framework developed by linking a global land surface models (LSMs)—that accounts for human land–water management activities—with its parent general circulation models (GCMs) to examine the extent of direct human influence on freshwater systems and climate over large scales
We subsequently highlight the importance of representing these human activities in global climate models and Earth system models to better simulate the coupled natural-human systems in the face of growing human influence on freshwater system and ongoing climate change

Summary

Introduction

Expanding human activities have profoundly affected various biophysical and biogeochemical processes of the Earth system over a broad range of scales, and freshwater systems are amongst the most extensively altered ecosystems (Postel et al 1996; Vitousek et al 1997; Nilsson et al 2005; Carpenter et al 2011). Human management of land and water resources began with the advent of settled agriculture ~10,000 years ago (Marsh and Lowenthal 1965; Postel 1999), but the pervasive alteration of freshwater systems through flow regulation and large-scale water diversion began to accelerate rapidly during the twentieth century as a result of proliferation in dam construction and widespread agricultural expansion to fulfill the growing needs for water, food, and energy for the global population that quadrupled in the past 100 years These large-scale water management practices have brought enormous benefits to our societies and resulted in an unprecedented scale of negative environmental consequences (Vitousek et al 1997; Postel et al 1996; Nilsson et al 2005; Micklin 2007; Rockström et al 2009; Carpenter et al 2011; Newbold et al 2016). Because of such widespread human perturbations of natural systems, it is not meaningful anymore to study freshwater systems and their interactions with climate without considering human activities (Oki and Kanae 2006)

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Results

Conclusion