Effect of spatial resolution of satellite images on estimating the greenness and evapotranspiration of urban green spaces

Abstract

Urban green spaces (UGS), like most managed land covers, are getting progressively affected by water scarcity and drought. Preserving, restoring and expanding UGS require sustainable management of green and blue water resources to fulfil evapotranspiration (ET) demand for green plant cover. The heterogeneity of UGS with high variation in their microclimates and irrigation practices builds up the complexity of ET estimation. In oversized UGS, areas too large to be measured with in situ ET methods, remote sensing (RS) approaches of ET measurement have the potential to estimate the actual ET. Often in situ approaches are not feasible or too expensive. We studied the effects of spatial resolution using different satellite images, with high‐, medium‐ and coarse‐spatial resolutions, on the greenness and ET of UGS using Vegetation Indices (VIs) and VI‐based ET, over a 780‐ha urban park in Adelaide, Australia. We validated ET with the ground‐based ET method of Soil Water Balance. Three sets of imagery from WorldView2, Landsat and MODIS, and three VIs including the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and Enhanced Vegetation Index 2 (EVI2), were used to assess long‐term changes of VIs and ET calculated from the different imagery acquired for this study (2011–2018). We found high correspondence between ET‐MODIS and ET‐Landsat (R2 > 0.99 for all VIs). Landsat‐VIs captured the seasonal changes of greenness better than MODIS‐VIs. We used artificial neural network (ANN) to relate the RS‐ET and ground data, and ET‐MODIS (EVI2) showed the highest correlation (R2 = 0.95 and MSE =0.01 for validation). We found a strong relationship between RS‐ET and in situ measurements, even though it was not explicable by simple regressions; black box models helped us to explore their correlation. The methodology used in this research makes a strong case for the value of remote sensing in estimating and managing ET of green spaces in water‐limited cities.

Riparian Area Changes in Greenness and Water Use on the Lower Colorado River in the USA from 2000 to 2020

“…Furthermore, we expect to produce results using EVI2 and ET(EVI2) methods on the urban regions within the LCR to contribute new information on how these urban green spaces affect reach level ecosystem health and water use [31]. These VI-based ET findings have been applied in Australian riparian zones [22] and to urban gardens [8,9]. Our future work includes comparing the unrestored riparian corridor on the LCR to the restoration sites initiated by Reclamation's Multi-Species Conservation Plan, an important study outside the scope of this research.…”

“…These tasks include scheduling for irrigation; sustaining agricultural production; securing foods and safe water quality and quantity for human uses; managing watersheds; allocating water; determining water rights; forecasting weather; and monitoring, managing, and projecting the long-term effects of land use change and global climate change on water resources [1][2][3][4][5]. Remotely sensed ET maps are useful for negotiating interstate and international water agreements, determining allocations for mining, urban use or natural resources managed by the U.S. Department of Interior, tribes and citizens, and for estimating water use by natural vegetation which creates habitat and requires protections for native and by invasive species [6][7][8][9][10]. Remotely sensed ET studies are often focused on agricultural water needs in drylands and importantly assess the impact of drought on consumptive water use [11][12][13].…”

Influence of Spatial Resolution on Remote Sensing-Based Irrigation Performance Assessment Using WaPOR Data

“…Several studies have investigated the relationship between spatial resolution or temporal resolution on accuracy of different input parameters [23,24] used to estimate irrigation performance by remote sensing-for example, normalized difference vegetation index (NDVI) [25,26], energy balance components [27], ETa [28], or net (NPP) or gross Primary Productivity (GPP) [29]. Further, much effort has been placed on continuously improving the resolution of these products [30] or aggregating images with varying resolutions to maximise information (i.e., aggregating high-spatial and low-temporal-resolution images with low-spatial and high-temporal-resolution images) [31].…”

Modelling hourly evapotranspiration in urban environments with SCOPE using open remote sensing and meteorological data

“…lives in cities (United Nations, 2019) and climate change is expected to further increase the frequency and intensity of heat islands (Huang et al, 2019), actions to mitigate the UHI effect are essential. Optimising ET capacity in urban areas could reduce extreme events such as severe heat waves, drought or flooding (Wang et al, 2020;Ward and Grimmond, 2017).Although ET is undeniably important for planning more sustainable cities, ET studies in urban environments are rare due to the challenges of measuring and modelling it in a highly heterogeneous landscape (Nouri et al, 2015(Nouri et al, , 2020.ET is a measurement of mass (millimetres) or energy (watts or joules) of the movement of water from the land surface to the atmosphere (i.e. liquid to vapour) (Liang and Wang, 2020).…”

“…Although ET is undeniably important for planning more sustainable cities, ET studies in urban environments are rare due to the challenges of measuring and modelling it in a highly heterogeneous landscape (Nouri et al, 2015(Nouri et al, , 2020.…”