Projections of future soil temperature in northeast Iran

Abstract

Soil temperature (Ts) is an important meteorological variable that noticeably impacts ecology, agriculture, and hydrology. In contrast to air temperature, there has been little focus on the projection of Ts in the future under climate change. In this study, future Ts were estimated at three weather stations (Ghoochan, Gonabad and Mashhad) in northeast Iran using an ensemble of 17 General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). These Ts were analyzed under different representative concentration pathway (RCP) scenarios by applying the Soil Temperature and Moisture Model (STM2). For each site, projected estimates were made for 10-year periods between 2025 and 2095, at depths of 5, 10, 20, 50, and 100 cm. Analysis of the data from the three stations yielded Ts increments ranging from 0.8 to 1.5 °C, 1.2–2.3 °C, and 2.4–4.4 °C, based on RCP scenarios RCP4.5, RCP6.0 and RCP8.5, respectively. Increased Ts may enhance crop development, especially during crop emergence and during parts of the vegetative period, but can also impact soil processes such as the rate of nutrient and CO2 release from soil organic matter, and the rate of evaporation. Due to this phenomenon, increased Ts can create faster and higher water deficits in soil, especially in arid to semi-arid climates. The method used in this study is applicable to diverse geographical contexts and the authors recommend similar studies be undertaken elsewhere in order to obtain further projected Ts data. The optimization of the current method may be particularly useful for future agro-climatological studies, as Ts impacts both plant and soil processes in addition to soil-atmosphere exchanges.