Watershed Management under Climate Change Scenarios. Case study: Maranhão watershed, Portugal.

Leonald Kalule

Key information

Authors:

Supervisors:

Ana Isabel Baião Ramos de Oliveira (Ana Isabel Baião Ramos de Oliveira); Ramiro Joaquim De Jesus Neves (Ramiro Joaquim De Jesus Neves)

Published in

09/26/2022

Abstract

Climate projections point to dryer and hotter Maranhão watershed in Eastern Portugal. MOHID Land model was used to quantify climate change's impact on the surface water, groundwaters, water balance and Maranhão reservoir's contribution to sustainable irrigation farming in Sorraia valley under RCPs 4.5 and 8.5 emission scenarios for near (2024-2039) and far (2075-2090) future. Compared with reference scenario (2001-2008), results indicated a 16% increase in streamflow under RCP4.5, 32% decrease under RCP8.5 in stream discharge, and 0.1 to 2m mean decrease in groundwater levels at temporal scale due to less precipitation hence recharge compared to discharge. Spatially, groundwater change ranged from -3.1 to 3.4m, with Northeastern Maranhão experiencing the most groundwater level decrease due to platy crystalline clay loams promoting lateral instead of vertical flow and subsequent recharge. Mean water balance error was 0.7%, indicating good MOHID Land capabilities at watershed scale water balance. The impact of climate change on water balance was quantified using evapotranspiration and outlet flow volume to precipitation (ETP:P and Q:P) ratios. Evapotranspiration process dominanted water extraction from the system. ETP:P generally increased whereas Q:P decreased. Plot scale irrigation needs predictions slightly increased due to increased transpiration requirements except the 0.2% decrease for olive trees in the near years being due to the methodology to which plant development considered heat units. With climate change (RCP8.5) related 19% decrease in Maranhão reservoir`s contribution to irrigation needs in near years and further 7% decrease in the long term, irrigation agriculture in Sorraia valley could be rendered unsustainable.