Credibility of Convection-Permitting Modeling to Improve Seasonal Precipitation Forecasting in the Southwestern United States

Abstract

Sub-seasonal to seasonal (S2S) forecasts are critical for planning and management decisions in multiple sectors. This study shows results from dynamical downscaling using a regional climate model at a convection-permitting scale driven by boundary conditions from the global reanalysis of the Climate Forecast System Model (CFSR). Convection-permitting modeling (CPM) enhances the representation of regional climate by better resolving the regional forcings and processes, associated with topography and land cover, in response to variability in the large-scale atmospheric circulation. We performed dynamically downscaled simulations with the Weather Research and Forecasting (WRF) model over the Upper and Lower Colorado basin at 12 km and 3 km grid spacing from 2000 to 2010 to investigate the potential of dynamical downscaling to improved the modeled representation of precipitation the Southwestern United States. Employing a convection-permitting nested domain of 3 km resolution significantly reduces the bias in mean (∼2 mm/day) and extreme (∼4 mm/day) summer precipitation when compared to coarser domain of 12 km resolution and coarse resolution CFSR products. The convection-permitting modeling product also better represents eastward propagation of organized convection due to mesoscale convective systems at a subdaily scale, which largely account for extreme summer rainfall during the North American monsoon. In the cool season both coarse and high-resolution simulations perform well with limited bias of ∼1 mm/day for the mean and ∼2 mm/day for the extreme precipitation. Significant correlation was found (∼0.85 for summer and ∼0.65 for winter) for both coarse and high-resolution model with observed regionally and seasonally averaged precipitation. Our findings suggest that the use of CPM is necessary in a dynamical modeling system for S2S prediction in this region, especially during the warm season when precipitation is mostly convectively driven.

Evaluating Multiple WRF Configurations and Forcing over the Northern Patagonian Icecap (NPI) and Baker River Basin

“…Zonal winds, on the other hand, influence seasonal air temperatures with a difference in mean temperature between summer and winter of 5 • C at the ice caps to 15 • C on the east side of west Patagonia [14]. The Baker River basin has an area of approximately 27,000 km 2 ; this basin produces the largest streamflow in Chile (>1000 m 3 •s −1 ) with significant contributions from glacier melting from the east side of the NPI. The Baker River Basin is one of the most diverse systems and data-sparse regions in the world, with precipitation ranging from 220 to 1707 mm per year and elevations changes of more than 3000 m in less than 60 km of distance [1].…”

“…In Figure 7, we show the performance of all the configurations in a box plot for ten stations. We also include lines for the three best configurations (lower bias) in wind speed that have acceptable results [44] in the stations around the Baker River (stations 3,4,8,9,10).…”

“…However, they cannot be used directly in watershed hydrology, since the resolution is not adequate. They can not resolve convective precipitation that occurs at smaller scales (around 4 km or less) [2,3]. To provide a higher resolution, we need to downscale the reanalysis data to a resolution that satisfies our needs.…”

High-resolution (1 km) Polar WRF output for 79° N Glacier and the northeast of Greenland from 2014 to 2018

“…In convection-permitting models, typically for spatial resolutions higher than 5 km, convection begins to be explicitly resolved. This can enhance the representation of convection and associated precipitation, as opposed to using a convection parameterization scheme (Pal et al, 2019). As of yet, there are no very high-resolution, multi-year atmospheric datasets available for the northeast of Greenland or the wider region.…”

Downscaling of seasonal ensemble forecasts to the convection‐permitting scale over the Horn of Africa using the WRF model

“…Smaller domains make the simulations affordable: regional climate models (RCM) at the convection‐permitting (CP) scale have been a common research tool in the last decade (Prein et al ., 2015). The advantages of CP models for seasonal climate modelling are lower biases and better skill scores (Schwitalla et al ., 2017; Pal et al ., 2019).…”