OPTIMUM REGIONAL IRRIGATION REQUIREMENTS UNDER CHANGING CLIMATE IN BULGARIA

Emil Dimitrov, Ivan Varlev, Mariya Ivanova, Zornitsa Popova

Abstract: Net irrigation requirements (NIR, mm) that fully satisfy crop development and yield formation are basic in irrigation systems’ design and management. Bulgarian practice usually adopts the irrigation scheduling developed by Zahariev et al. (1986) that provide information on 31 crops and 97 irrigation regions (IR). Years, having probability of occurrence of an irrigation depth PI=10, PI=25 and PI=50%, were considered. To cope with climate uncertainties and drought aggravation, simulations were performed for past (1950-1980) and present (1951-2004) weather conditions of unified Agro-Climatic AC regions. In former studies the irrigation scheduling simulation WinISAREG model was calibrated for maize using data from long-term experiments carried out in fields of diverse soil, climate and management conditions. Optimal AC regions were defined on the grounds of average reference evapotranspiration totals for July-August relative to the period 1951-2004 EToJul-Aug. Thus, EToJul-Aug served as an indicator of regional NIR and IR unification into AC regions. The impacts of soil properties were characterised by total available soil water TAW, being “small” if TAW=116, “average” if 136<TAW<157 and “large” when 173<TAW<180 mm m-1. NIR were computed by model application to soils of small and large TAW in each AC region and 1951-2004 period. Results indicate that when EToJul-Aug increases from 260 to 330 mm, NIR in “average” demand year (PI=50%) increase from 160 to 310 mm for soils of “small” TAW. Relative to 1951-1980, unified conventional irrigation demands were compared to those simulated. Results showed that the former were mostly in the range of those derived by model simulations. It was concluded that the model took better into account the impact of climate change and different TAW. Maps illustrate findings of the study over country territory in “an average”, “a moderately dry” and “a very dry” season.

Keywords: Climate Change; ETo; Regional irrigation requirements; WinISAREG model

Date published: 2018-06-01