Assessing Climate Change Impacts on Streamflow, Sediment and Nutrient Loadings of the Minija River (Lithuania): A Hillslope Watershed Discretization Application with High-Resolution Spatial Inputs

Natalja Čerkasova,Georg Umgiesser,Ali Ertürk

doi:10.3390/w11040676

Natalja Čerkasova, Georg Umgiesser + Show 1 more

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https://doi.org/10.3390/w11040676

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Abstract

In this paper we focus on the model setup scheme for medium-size watershed with high resolution, multi-site calibration, and present results on the possible changes of the Minija River in flow, sediment load, total nitrogen (TN), and total phosphorus (TP) load in the near-term (up to 2050) and long-term (up to 2099) in the light of climate change (RCP 4.5 and RCP 8.5 scenarios) under business-as-usual conditions. The SWAT model for the Minija River basin was setup by using the developed Matlab (SWAT-LAB) scripts for a highly customized watershed configuration that addresses the specific needs of the project objective. We performed the watershed delineation by combining sub-basin and hillslope discretization schemes. We defined the HRUs by aggregating the topographic, land use, soil, and administrative unit features of the area. A multisite manual calibration approach was adopted to calibrate and validate the model, achieving good to satisfactory results across different sub-basins of the area for flow, sediments and nutrient loads (TP and TN). After completing the climate change scenario calculations, we found that a net decrease of flow (up to 35%), TN (up to 34%), and TP (up to 50%) loads are projected under both scenarios. Furthermore, we explored the changes in the streamflow composition and provide new insight on the reason of projected nutrient load decrease.

Highlights

The recent State of the Baltic Sea report [1] shows that more than 97% of the Baltic Sea area suffers from eutrophication due to past and present excessive inputs of nitrogen and phosphorus
The calibration procedure followed the general recommendations for Soil and Water Assessment Tool (SWAT) model calibration [56], where one starts with flow calibration, sediment and, nutrients
This study of the Minija River basin is a contribution to the fine-grid large-scale model development, where the ultimate goal is to assess the entire Nemunas River watershed in terms of hydrology, nutrient, and sediment loads under a changing climate

Summary

Introduction

The recent State of the Baltic Sea report [1] shows that more than 97% of the Baltic Sea area suffers from eutrophication due to past and present excessive inputs of nitrogen and phosphorus. Owing to the implementation of the Baltic Sea Action Plan [2] by the Baltic Marine Environment Protection. According to the assessment of progress towards the national targets for input of nutrients achieved by 2014 [3], Lithuania, as a HELCOM member, has yet to reduce the inputs to the maximum allowable levels, though the country has made some progress; for example, Lithuania was the only country that reduced total phosphorus inputs to all sub-basins to which it contributes [3]. Adaptation to climate change is a central issue for the planning and implementation of measures to reduce nutrient inputs, as well as for adjusting the level of nutrient input reductions to ensure protection of the Baltic Sea marine environment in a changing climate. The maximum allowable inputs calculated under assumptionthat thatthe theBaltic

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