RESUMO
Overexploitation of water resources has led to severe ecological degradation and even desertification in some arid inland river basins, northwestern China. To alleviate or restore the degraded vegetation ecosystem, ecological water conveyance (EWC) has become an important and effective measure. Scientific assessment of the impact of EWC on vegetation restoration and determination of the corresponding optimal EWC volume (EWCV) are important to formulate rational ecological water management. In this study, long time series normalized difference vegetation index (NDVI) was used to extract the restored vegetation area in Qingtu Lake area, a terminal lake in inland Shiyang River basin, northwestern China. The relationship between restored vegetation coverage and EWC was explored to determine the optimal EWCV. The restored vegetation area (RVA) increased dramatically in the first five years and became stable from 2016. The time lag of the response of RVA increase to EWC was about 2 years. A bell-shaped function between RVA and groundwater depth was obtained based on the results from Unmanned Aerial Vehicle (UAV) and micro terrain of the lake area. Based on the fitted function, five groundwater depth thresholds were obtained. The optimal groundwater depth in the hydrometric station was 2.91 ± 0.09 m for the maximal RVA (17.08 ± 3.25 km2). A polynomial function between the yearly EWCV and groundwater depth was developed and the EWCV thresholds corresponding to the groundwater depth thresholds were estimated. The optimal EWCV into Qingtu Lake was 2224.4 × 104 m3 for the maximal RVA. The correspondingly optimal EWCV from Hongyashan Reservoir was 3271.4 × 104 m3. The spatial distribution patterns of remotely sensed water surface and NDVI suggested that expanding the water-receiving area of conveyed water was useful to improve the vegetation growth. This study provides a reference for assessing the impact of EWC on vegetation restoration and determining the correspondingly optimal EWCV in arid inland river basins.
RESUMO
In the first two decades of the 21st century, 79 global big cities have suffered extensively from drought disaster. Meanwhile, climate change has magnified urban drought in both frequency and severity, putting tremendous pressure on a city's water supply. Therefore, tackling the challenges of urban drought is an integral part of achieving the targets set in at least 5 different Sustainable Development Goals (SDGs). Yet, the current literatures on drought have not placed sufficient emphasis on urban drought challenge in achieving the United Nations' 2030 Agenda for Sustainable Development. This review is intended to fill this knowledge gap by identifying the key concepts behind urban drought, including the definition, occurrence, characteristics, formation, and impacts. Then, four sub-categories of urban drought are proposed, including precipitation-induced, runoff-induced, pollution-induced, and demand-induced urban droughts. These sub-categories can support city stakeholders in taking drought mitigation actions and advancing the following SDGs: SDG 6 "Clean water and sanitation", SDG 11 "Sustainable cities and communities", SDG 12 "Responsible production and consumption", SDG 13 "Climate actions", and SDG 15 "Life on land". To further support cities in taking concrete actions in reaching the listed SDGs, this perspective proposes five actions that city stakeholders can undertake in enhancing drought resilience and preparedness:1) Raising public awareness on water right and water saving; 2) Fostering flexible reliable, and integrated urban water supply; 3) Improving efficiency of urban water management; 4) Investing in sustainability science research for urban drought; and 5) Strengthening resilience efforts via international cooperation. In short, this review contains a wealth of insights on urban drought and highlights the intrinsic connections between drought resilience and the 2030 SDGs. It also proposes five action steps for policymakers and city stakeholders that would support them in taking the first step to combat and mitigate the impacts of urban droughts.
