Drought Recovery: Quantifying Climate and Environmental Factors

Abstract

Drought, characterised by prolonged periods of below-normal water availability, has intensified in recent decades due to climate change, with rising temperatures and reduced precipitation exacerbating its severity. South America has been particularly affected, with countries such as Chile, Argentina, and Brazil experiencing prolonged droughts, resulting in severe economic and ecological consequences. Chile alone faced losses exceeding US$5.4 billion (2010–2020) due to multi-year droughts, which were worsened by secondary effects, including wildfires that burnt 640,000 hectares in 2017. The growing societal vulnerability to drought underscores the need for improved understanding of drought development and recovery to inform better water management strategies. This thesis investigates drought recovery mechanisms in different ecosystems, focusing on the Southern Andes and Central Chile. It examines hydrological and ecological factors influencing recovery, utilising data analysis and modelling to assess surface water and groundwater dynamics under natural and anthropogenic influences. The research aims to identify key drivers of drought recovery and develop a modelling framework to enhance drought resilience. Chile’s diverse geography, featuring mountains, valleys, and coastal regions, presents unique challenges due to declining precipitation and endangered endemic species. Tree-ring analysis is employed to study long-term drought impacts on vegetation. Chapter 2 introduces the study area and its hydrological characteristics, while Chapter 3 uses the PCR-GLOBWB2.0 model to evaluate anthropogenic effects, particularly irrigated agriculture, on groundwater. Findings highlight unsustainable groundwater withdrawals altering recharge patterns, emphasising the need to incorporate lateral groundwater flow in drought assessments. Accurate water abstraction data and land-use considerations are crucial for modelling drought recovery. Chapter 4 utilises the CAMELS-CL dataset to analyse discharge drought recovery across Chilean basins. Results show that precipitation and snowmelt are critical for recovery, while vegetation recovery depends on catchment storage-release dynamics and water extraction. Soil moisture recovery is linked to precipitation elasticity and groundwater interactions. Although common factors (e.g., snow accumulation) influence recovery, local conditions make recovery rates site-specific. Chapter 5 presents CONDOR, a dataset compiling tree-ring width (TRW) data from 180 trees across semi-arid to Mediterranean regions in the Southern Andes. This resource helps track historical drought impacts on vegetation, integrating with broader hydrological research. Chapter 6 examines Mediterranean forests in Chile, revealing declining vegetation health due to reduced rainfall and higher temperatures. Since the early 2000s, South America’s carbon uptake has reversed due to drying trends, with precipitation now the dominant climatic factor affecting vegetation, more so than temperature. Key conclusions suggest that regional hydrological frameworks and streamflow observations improve drought recovery analysis. Anthropogenic water use and catchment characteristics significantly shape recovery rates, necessitating integrated water management strategies. The thesis highlights the need to address climatic variability, human-induced drought, and multi-scale resilience planning to balance ecological and societal water demands. By combining tree-ring data, remote sensing, and hydrological modelling, this research advances understanding of long-term drought impacts on ecosystems, providing insights for sustainable water management in drought-prone regions.