Evaluation of three new surface irrigation parameterizations in the WRF-ARW v3.8.1 model: the Po Valley (Italy) case study

Abstract

Abstract. Irrigation is one of the land managements that can affect the local climate. Recent literature shows that it affects mostly the near-surface variables and it is associated with an irrigation cooling effect. However, there is no common parameterization that also accounts for a realistic water amount, and these factors could be ascribed as causes of different impacts found in previous studies. This work aims to develop three new surface irrigation parameterizations within the WRF-ARW model (V3.8.1) that consider different evaporative processes. The parameterizations are tested on one of the regions where global studies disagree on the signal of irrigation: the Mediterranean area, and in particular the Po Valley. Three sets of experiments are performed using the same irrigation water amount of 5.7 mm/d, derived from Eurostat data. Two complementary validations are performed for July 2015: monthly mean, minimum and maximum temperature with ground stations and potential evapotranspiration with the MODIS product. All tests show that both mean and maximum temperature, as well as potential evapotranspiration, simulated fields approximate better the measures when using the irrigation parameterizations. This study addresses the sensitivity of the results to the parameterizations' human-decision assumptions: start time, length and frequency. The main impact of irrigation on surface variables such as soil moisture is due to the parameterization choice itself, rather than the timing. Moreover, on average, the atmosphere and soil variables are not very sensitive to the parameterizations assumptions for realistic timing and length.

Regional Climate Impacts of Irrigation in Northern Italy Using a High Resolution Model

“…This study is based on the assumptions and simulation described in Valmassoi et al [43]. More is summarized in this and the following sections.…”

“…The main reason given is because the signal is not masked by precipitation or larger scale systems. Our previous studies describe the choice of the period and its climatic characterization in terms of temperature and precipitation anomalies [43]. The reason for choosing the summer of 2015, with its July heat wave, instead of the more severe heat wave year of 2003 is due to the irrigation context.…”

“…This work employs the same simulations as described previously in Valmassoi et al [43], and a brief summary is given below. The driving models used to create the initial and boundary conditions are from different models for the soil and atmosphere.…”

“…The WRF single-moment 6-classes (WSM6) microphysics scheme [52] and the Yonsei University (YSU) boundary layer parameterization [53] are used. For more on the parameterization choices refer to Valmassoi et al [43].…”

“…Also, most of the used parameterizations do not account for the water applied explicitly [11,12,41,42], leading to an overestimation of the total amount [16,26]. The newly developed parameterization for WRF resembles several irrigation techniques with different evaporative components from the water applied, as well as an explicit treatment of both water used and timing [43].…”