On the diurnal cycle of surface energy fluxes in the North American monsoon region using the WRF‐Hydro modeling system

Abstract

The diurnal cycles of surface energy fluxes are important drivers of atmospheric boundary layer development and convective precipitation, particularly in regions with heterogeneous land surface conditions such as those under the influence of the North American monsoon (NAM). Characterization of diurnal surface fluxes and their controls has not been well constrained due to the paucity of observations in the NAM region. In this study, we evaluate the performance of the uncoupled WRF‐Hydro modeling system in its ability to represent soil moisture, turbulent heat fluxes, and surface temperature observations and compare these to operational analyses from other commonly used land surface models (LSMs). After a rigorous model evaluation, we quantify how the diurnal cycles of surface energy fluxes vary during the warm season for the major ecosystems in a regional basin. We find that the diurnal cycle of latent heat flux is more sensitive to ecosystem type than sensible heat flux due to the response of plant transpiration to variations in soil water content. Furthermore, the peak timing of precipitation affects the shape and magnitude of the diurnal cycle of plant transpiration in water‐stressed ecosystems, inducing mesoscale heterogeneity in land surface conditions between the major ecosystems within the basin. Comparisons to other LSMs indicate that ecosystem differences in the diurnal cycle of turbulent fluxes are underestimated in these products. While this study shows how land surface heterogeneity affects the simulated diurnal cycle of turbulent fluxes, additional coupled modeling efforts are needed to identify the potential impacts of these spatial differences on convective precipitation.

Influence of initial soil moisture and vegetation conditions on monsoon precipitation events in northwest México

“…The RSB is a north-south oriented watershed (21 264 km 2 ) with mean annual precipitation ranging from 350 to 700 mm (Hallack-Alegria and Watkins, 2007) of which 40 to 70% falls during the NAM from July to September . The mountainous terrain within the RSB exhibits a relief of more than 2000 m, leading to spatial heterogeneities in soil texture and vegetation distributions in the basin (e.g., Robles-Morua et al, 2015;Xiang et al, 2017). Prior land surface modeling studies have built a solid foundation on the simulation of hydrologic and ecosystems processes in the RSB (e.g., Vivoni et al, 2010;Robles-Morua et al, 2012;Xiang et al, 2014;Mascaro et al, 2015) allowing for the detailed coupled land-atmosphere modeling experiments conducted in this work.…”

“…For each time step of Domain 3, land surface model states and fluxes (e.g., soil moisture content for each soil layer, lateral runoff) are exchanged between Noah-MP (1 km resolution) and a disaggregated overland and river routing scheme (100 m resolution). Additional details on the setup of the coupled land surface and routing schemes in WRF-Hydro are provided by and Xiang et al (2017).…”

“…The atmosphere is simulated using 44 vertical layers with the top level set to 100 hPa. As a recent development, WRF-Hydro integrates multiple land surface representations within WRF to improve its ability to represent distributed hydrologic processes, including overland flow routing, subsurface transport, river routing and the impacts of reservoirs Yucel et al, 2015;Senatore et al, 2015;Xiang et al, 2017). Here, the Noah with multi-parameterization (Noah-MP, Niu et al, 2011) land surface scheme is adopted to simulate water and energy fluxes in each two-way nested domain (Fig.…”

“…Finally, disentangling the independent feedback effects of soil moisture and vegetation greenness on precipitation using observations is difficult given their high correlation (Méndez-Barroso et al, 2009. Thus, building on prior observational efforts and land surface modeling studies (e.g., Vivoni et al, 2007Xiang et al, 2014Xiang et al, , 2017, we conduct fully-coupled land-atmosphere simulations using the WRF-Hydro modeling system to represent the independent effects of initial soil moisture and vegetation conditions on precipitation without consideration of the potential synergies between these initial states. This is achieved by first carrying out a set of WRF-Hydro 'baseline' simulations in two summers (July-August of 2004 and 2013) selected based on synoptic conditions and data availability in a large watershed in northwest México.…”

“…This is achieved by first carrying out a set of WRF-Hydro 'baseline' simulations in two summers (July-August of 2004 and 2013) selected based on synoptic conditions and data availability in a large watershed in northwest México. The baseline simulations are compared to both reanalysis products and the offline (uncoupled) WRF-Hydro simulations of Xiang et al (2017). Subsequently, sets of short-term (72 h) experiments are conducted using different initial soil moisture and vegetation conditions for four selected storm periods to diagnose the occurrence and magnitude of the feedback processes.…”