Assessing Climate and Land Changes in a Himalayan Watershed

Jim Crocker
23rd February, 2024

Assessing Climate and Land Changes in a Himalayan Watershed

Puthimari River

Photo adapted from: AMNR0011 / CC BY SA (Source)
Flooding is a recurring problem for many regions, particularly those with monsoon climates and complex river systems. Understanding how climate change and human activity will affect river flows is crucial for effective flood management and water resource planning. Recent research from the National Institute of Hydrology (India)[1] focuses on the Puthimari River, a tributary of the Brahmaputra, which frequently causes downstream flooding during the monsoon season. The study aims to predict how the river’s discharge – the volume of water flowing through it – will change by the end of the century, considering both climate change and alterations to land use. The research team used a computer model called the Soil and Water Assessment Tool (SWAT) to simulate the river’s behaviour. SWAT is a widely used hydrological model that accounts for various factors influencing water flow, including rainfall, temperature, land cover, and soil characteristics. The model was tested for accuracy using historical data, achieving high levels of reliability as indicated by Nash-Sutcliffe efficiency (NSE) and coefficient of determination (R2) values of 0.74/0.77 and 0.75/0.79 respectively for calibration and validation. This means the model accurately reflects the river’s past behaviour, increasing confidence in its future predictions. The study considered two potential future climate scenarios, known as Representative Concentration Pathways (RCPs). RCP4.5 represents a moderate increase in greenhouse gas emissions, while RCP8.5 represents a much higher increase. Future climate data from five different climate models were used for each scenario. Simultaneously, the researchers projected changes in land use and land cover (LULCC) – how land is used for things like agriculture, forests, and settlements – using a model that predicts future patterns based on past trends. These projections indicated significant changes: a 19.76% increase in rural settlements, coupled with declines in forest cover (6.30%), cropland (16.45%), and water bodies (8.76%) by the end of the century. The results show a clear link between climate change, land use changes, and increased river discharge. Under the moderate emissions scenario (RCP4.5), average monsoon rainfall is projected to increase by 14.16%, leading to a 34.27% increase in the Puthimari River’s discharge. Under the higher emissions scenario (RCP8.5), the rainfall increase is even more substantial at 38.92%, resulting in a 64.67% increase in discharge. This suggests that increased rainfall, combined with changes in the landscape, will exacerbate flooding risks in the region. These findings align with broader observations of changing rainfall patterns and their impact on water resources. For example, research in India[2] has highlighted an increasing spatial variability in extreme rainfall events, even as the overall mean monsoon rainfall shows decreasing spatial variability. This means that while average rainfall might not change dramatically across the entire country, the intensity and location of heavy rainfall events are becoming more unpredictable. The Puthimari study builds on this by demonstrating how these changes translate into increased river discharge and potential flooding. Furthermore, the impact of land use change on river flow is consistent with observations from other regions. A study on the Mississippi River[3] found that increased discharge from agricultural watersheds, driven by land use changes, was a major factor in rising bicarbonate flux – a measure of dissolved minerals – and nutrient runoff. Similarly, research in Nagaland, India[4] documented significant increases in built-up areas and declines in forest cover, leading to increased flood risk. The Puthimari study reinforces the idea that alterations to land cover can significantly influence hydrological processes. Interestingly, the Puthimari research contrasts with some previous assumptions about climate change impacts. A study examining the Kibungo sub-catchment[5] found that while rainfall was decreasing, water yield was increasing in deficit basins, challenging the notion that dry areas simply become drier. The Puthimari study, however, demonstrates a scenario where increased rainfall, coupled with land use changes, leads to increased discharge, potentially exacerbating flooding in downstream areas. This highlights the importance of considering regional variations and the interplay between different factors when assessing climate change impacts. The research provides valuable information for policymakers and government agencies responsible for managing water resources and mitigating flood risks. The detailed projections of future river discharge can inform the design of structural measures, such as dams and levees, as well as non-structural measures, like improved flood forecasting and land use planning. Effective watershed management practices, informed by these findings, are also crucial for safeguarding the Puthimari River and the communities that depend on it.

AgricultureEnvironmentEcology

References

Main Study

1) A combined impact assessment of climate and land use/land cover change in an Eastern Himalayan watershed in northeast India.

Published 22nd February, 2024

https://doi.org/10.1007/s10661-024-12433-4

Related Studies

2) Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes.

https://doi.org/10.1371/journal.pone.0158670

3) Anthropogenically enhanced fluxes of water and carbon from the Mississippi River.

https://doi.org/10.1038/nature06505

4) Monitoring land use land cover changes in the Eastern Himalayan landscape of Nagaland, Northeast India.

https://doi.org/10.1007/s10661-020-08674-8

5) Impacts of climate and land use/cover changes on streamflow at Kibungo sub-catchment, Tanzania.

https://doi.org/10.1016/j.heliyon.2022.e11285


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