Assessing Regcm4 simulations of the diurnal temperature range over Egypt: sensitivity to soil moisture initialization and land-surface parameterization

Abstract

This study investigates the impact of soil moisture initialization and land-surface parameterization on Egypt’s diurnal temperature range (DTR) using the regional climate model RegCM4. Four 40-year simulations were conducted for the period 1979–2018, representing different combinations of soil moisture datasets and hydrological schemes. Soil moisture was initialized using two products: the ESA Climate Change Initiative (ESA) satellite dataset and the Century (CEN) reanalysis dataset. In addition, two hydrological schemes were applied: TOPMODEL (TOP) and the Variable Infiltration Capacity model (VIC). All simulations were evaluated against the high-resolution TerraClimate dataset and in-situ station observations. The results indicate that daily maximum temperature (TMX) is largely insensitive to both soil moisture initialization and parameterization schemes, whereas daily minimum temperature (TMN) and DTR exhibit strong sensitivity. Simulations initialized with the ESA dataset generally produce warmer TMN values than those initialized with the CEN dataset, with biases ranging from 2–4°C along the Mediterranean coast and 2–6°C across much of Egypt. A similar sensitivity is observed between the TOP and VIC hydrological schemes. Overall, the CEN–TOP configuration provides the most accurate simulation of DTR across all seasons. Comparison with station observations reveals that DTR biases vary by location, with both overestimation and underestimation depending on the station. Application of a linear scaling (LS) bias-correction method significantly reduces these biases. These findings suggest that accurate simulation of Egypt’s DTR can be achieved when RegCM4 is initialized with the CEN soil moisture dataset, coupled with the TOP hydrological scheme, and corrected using LS. Received: 09 March 2026 Accepted: 05 April 2026 Published: 19 May 2026