Upstream-downstream linkages of hydrological processes in the Himalayan region

Santosh Nepal,Arun Bhakta Shrestha,Wolfgang-Albert Flügel

doi:10.1186/s13717-014-0019-4

Abstract

Understanding the upstream-downstream linkages in hydrological processes is essential for water resources planning in river basins. Although there are many studies of individual aspects of these processes in the Himalayan region, studies along the length of the basins are limited. This study summarizes the present state of knowledge about linkages in hydrological processes between upstream and downstream areas of river basins in the Himalayan region based on a literature review. The paper studies the linkages between the changes in the physical environment of upstream areas (land use, snow storage, and soil erosion) and of climate change on the downstream water availability, flood and dry season flow, and erosion and sedimentation. It is argued that these linkages are complex due to the extreme altitudinal range associated with the young and fragile geology, extreme seasonal and spatial variation in rainfall, and diversity of anthropogenic processes. Based on the findings, the paper concludes that integrated systems analysis is required to understand the holistic complexity of upstream-downstream linkages of hydrological processes in the river basin context. The integrated land and water resources management (ILWRM) approach can be instrumental in developing adaptive solutions to problems and can also enable stakeholders of upstream and downstream areas with various interests and needs to work together for the better utilization and management of land and water resources. As a part of this, the specific circumstances of the upstream communities, who live in fragile and inaccessible mountain areas with limited resource opportunities, should be taken into account so that incentive mechanisms can be established to encourage and acknowledge their contribution.

Highlights

In a river basin, hydrological events that occur in the upper part may have a direct influence downstream (Nepal 2012), from a few to many hundreds of kilometers away
Upstream impacts on hydrological processes can be broadly divided into two types: (i) human-influenced activities related to land use and (ii) natural impacts related to climate (Nepal 2012)
The role of forest and other vegetation in, and the impacts of deforestation and cultivation on, runoff, base flow, and soil erosion are complex, and it is important not to draw conclusions from results focused on individual aspects of the process

Summary

Introduction

Hydrological events that occur in the upper part may have a direct influence downstream (Nepal 2012), from a few to many hundreds of kilometers away. This review focuses on synthesizing the available information on upstream-downstream linkages related to hydrological processes in the Himalayan region; in particular, the impacts of climate and land use changes on water quantity and sediment transport. Impat (1981) and Ramsay (1987) summarized the literature on measured rates of surface erosion in Nepalese mountains and found high rates of surface erosion under various circumstances with considerable differences between land use types, e.g., overgrazed pasture (9.85 t/ha), protected pasture (1 t/ha), and forest (0.43 t/ha) Most of these studies reflect the condition and processes in the small-scale catchments in the transition zone of the region's rivers. Water supplies will be affected by the projected increase in evapotranspiration resulting from the increase in temperature and reduction in winter season precipitation (Mu et al 2013) leading to reduced runoff, increased abstraction of water for irrigation, and reduced flow

Findings

Discussion

Conclusions