Towards sustainable land and water management: Eco-hydrological and global scale modelling

Abstract

More than 40% of the Earth’ surface is covered by drylands which are home to nearly three billion people. Climate change and over-pressure on land and water resources as a result of population growth have endangered the ecosystem functioning in drylands. Ecosystem degradation could adversely affect people’s livelihoods and well-being. This study helps with decision-making to address two land and water resources managerial challenges in drylands: desiccating saline lakes and soil salinization. Saline lakes as the main natural aquatic feature of dryland landscapes are desiccating at alarming rates in the recent decades, predominantly due to human interventions and climate change. The result is increased water salinity levels which negatively impacts the ecosystems integrity in the nearby regions. To sustainably restore and preserve the saline lakes in the short- (e.g. 10 years) and long-term periods (e.g. 30 years), a four-step eco-hydrological framework, primarily based on land use strategies is proposed here: (1) projecting the future governing climatic patterns in the basin under study; (2) evaluating the needed water for restoration of the saline lake; (3) prioritising and allocation of the water to all environmental, municipal, industrial, and agricultural water users; and (4) optimisation of the agricultural land use considering the total available land and freshwater resources. The applicability of the framework was examined by the case of Lake Urmia in Iran — known formerly as the second (by volume) hyper-saline lake in the world. The results show that for restoration of Lake Urmia, annually 3,648 Mm3 (∼70% increase) and 3,692 Mm3 (∼73% increase) surface water inflow to the lake is required to restore the lake in 30 years under the two greenhouse gases emission scenarios of RCP 4.5 and RCP 8.5, respectively. Provision of these inflow volumes needs respective reductions of 95,600 ha and 133,687 ha in the Urmia basin irrigated area. The proposed framework can inform decision-making for adapting and enhancing the resilience of the saline lakes to negative consequences of the over-exploitation of water resources, particularly in the context of projected climate change. The second part of this research estimates the extent, severity, and long-term trends in soil salinization as one of the land degrading threats in drylands. Soil salinization is a dynamic and common environmental issue; however, there remains considerable uncertainties regarding its large-scale spatio-temporal variability and relation to the future climate change. Due to unavailability of the detailed soil and plant data for application of physical- or numerical-based methods, Machine Learning (ML) techniques were used for prediction of the soil salinization trends on a global scale. Using the ML techniques, measured legacy soil profile data were related to a set of environmental predictors to estimate the soil salinity (and sodicity where Na+ is higher compared to other soluble salts) at other locations, depths, and times. With a similar approach and based on outputs of the Global Circulation Models, the trends in drylands’ soil salinization were predicted to the end of the 21st century. Between 1980 and 2018, the results indicate that soil salinity and sodicity have been temporally and geographically highly variable. Additionally, compared to the 1961 - 1990 period, the results show that primary (naturally-occurring) soil salinity will be a major issue in the drylands of South America, southern and Western Australia, Mexico, southwest United States, and South Africa by the end of the 21st century. The results provided by this study could contribute to sustainable land and water management in dryland regions of the world.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Adisa Azapagic (Supervisor) & Nima Shokri (Supervisor)