Modeling the Climate and Land Cover Change Effects on Urban Water and Energy Dynamics in the Phoenix Metropolitan Area

The Phoenix Metropolitan Area (PMA) has grown from a small agricultural center to a major metropolis and still ranks among the fastest growing cities in the U.S. Urbanization is known to impact water and energy dynamics due to changes in impervious cover, stormwater infrastructure and landscaping. Meanwhile, increasing extreme events such as heat waves and floods interact with land use and land cover (LULC) change, highlighting the importance of city planning, infrastructure development and mitigation actions. Recent progress on the Integrated Climate and Land-Use Scenarios (ICLUS) product provides an opportunity to investigate the effects of future LULC change on urban hydroclimatic dynamics. Similarly, local practitioners in the PMA have developed LULC scenarios under different sustainable strategies. Using these diverse scenarios built at national and city levels, we apply the Variable Infiltration Capacity (VIC) land surface hydrology model and a river routing model at 1-km resolution under historical (2000-2010) and future climate and land use conditions (2030-2060). We use statistically-downscaled future forcings from a set of climate models selected based on model performance in the historical period. We calculate the impervious cover percentage for developed land use categories from the 30-m National Land Cover Database and estimate irrigation water usage from vegetation mapping at high-resolution (1-m) and published irrigation water requirements. For routing purposes, we modify local topography with the locations irrigation canals and stormwater drainage channels that modify runoff during storms. Routing parameters are calculated for different land covers according to design guidelines in the PMA. For this work, we use land surface temperature (LST) as a VIC calibration target due to the influence of urbanization on its spatiotemporal distribution and the availability of remote sensing products (Moderate Resolution Imaging Spectroradiometer at 1 km resolution) and ground observations. We test the ability of VIC in reproducing LST pattern in the historical period, finding good agreement. With confidence built in the historical simulation, we investigate the effects of land cover and climate changes on LST in the future scenarios. First, we correlate the LST spatial distribution pattern with the land use and impervious cover percentage. With the fine-resolution land use map, we tabulate the fraction of urban components (soil, road, building, vegetation, and water) for all built-up classes and identify the main causes of LST variance between different categories. We compare the ICLUS scenarios, based on assumptions of population growth for the year 2060, to the stakeholder-generated scenarios (adaptive, strategic, and transformative) to evaluate the effectiveness of different sustainable strategies in solving future heat problems (e.g. remove impervious surface and increase green canopy cover). In this way, we can provide information to city planners and decision makers on the selection of sustainable development policies from a numerical modeling perspective.