Risk Assessment of Climate Change and Droughts in the Zone of Chernozems, North Bulgaria
Z. Popova, М. Ivanova, L. S. Pereira, K. Boneva, K. Doneva, V. Alexandrov, M. Kercheva, P. Alexandrova
Abstract: This study aims at assessing drought and related climate change trends as well as their impacts on agriculture in North Bulgaria. Trend tests were applied to climate data, mainly precipitation, temperature and reference evapotranspiration (ETo) relative to selected weather stations.
Results of the Mann-Kendall trend test show significant positive trends for maximum temperature in May, June, July and particularly an increase trend in annual Tmax by 0.02 mm yr-1 at Varna, Lom and Silistra. Relative to ETo for the maize crop season “May-Sept”, a significant trend was observed for the period 1970 – 2004. The detected increase of seasonal ETo is 1.0 mm yr-1 at Silistra, up to 2.3 mm yr-1 at Pleven and Lom, reaching a maximum of 2.6 mm yr-1 at Varna. The magnitude of this trend is about half if one considers the whole 1951 – 2004 period instead of 1970 – 2004, which indicates that the aggravation of climate conditions is higher in recent times.
The WINISAREG simulation model was previously calibrated and validated using independent field data from long-term irrigation experiments with late and semi-early maize hybrids for various locations and soils with small, medium and large total available water (TAW). Thus the model could be applied with appropriate accuracy to compute yield impacts of water stress and irrigation requirements for the 1951 – 2004 period. Rainfed maize in the Danube Plain is associated with some yield variability (33% < Cv < 54%) that is in fact smaller than in the Thracian Lowland (40% < Cv < 70%). Nevertheless that drought impact is mitigated in North Bulgaria it is a key factor in some regions (Lom and Varna). Basing upon economic considerations, relative yield decreases (RYD) were computed with the threshold of 67, 55 and 60% of the potential maize productivity in Pleven, Lom and Silistra. Maize production is risky in 22% of years in Lom when TAW is large, which is the double of risk in Pleven and Silistra. If TAW is medium the risky years double and reach 50% of years in Varna.
The application of the trend analyses to net irrigation requirements NIR over the 1970 – 2004 period shows a significant increase of NIR by 120 (Pleven), 90 – 80 mm (Lom, Silistra) that is half than in Varna. Contrarily, water stress increase related to the raifed maize led to yield decrease on drylands by 32% of potential yield on the average in Pleven, by 20% in Lom and Silistra and by 10% in Varna thus indicating that innovative risk approaches are required.
Results of the Mann-Kendall trend test show significant positive trends for maximum temperature in May, June, July and particularly an increase trend in annual Tmax by 0.02 mm yr-1 at Varna, Lom and Silistra. Relative to ETo for the maize crop season “May-Sept”, a significant trend was observed for the period 1970 – 2004. The detected increase of seasonal ETo is 1.0 mm yr-1 at Silistra, up to 2.3 mm yr-1 at Pleven and Lom, reaching a maximum of 2.6 mm yr-1 at Varna. The magnitude of this trend is about half if one considers the whole 1951 – 2004 period instead of 1970 – 2004, which indicates that the aggravation of climate conditions is higher in recent times.
The WINISAREG simulation model was previously calibrated and validated using independent field data from long-term irrigation experiments with late and semi-early maize hybrids for various locations and soils with small, medium and large total available water (TAW). Thus the model could be applied with appropriate accuracy to compute yield impacts of water stress and irrigation requirements for the 1951 – 2004 period. Rainfed maize in the Danube Plain is associated with some yield variability (33% < Cv < 54%) that is in fact smaller than in the Thracian Lowland (40% < Cv < 70%). Nevertheless that drought impact is mitigated in North Bulgaria it is a key factor in some regions (Lom and Varna). Basing upon economic considerations, relative yield decreases (RYD) were computed with the threshold of 67, 55 and 60% of the potential maize productivity in Pleven, Lom and Silistra. Maize production is risky in 22% of years in Lom when TAW is large, which is the double of risk in Pleven and Silistra. If TAW is medium the risky years double and reach 50% of years in Varna.
The application of the trend analyses to net irrigation requirements NIR over the 1970 – 2004 period shows a significant increase of NIR by 120 (Pleven), 90 – 80 mm (Lom, Silistra) that is half than in Varna. Contrarily, water stress increase related to the raifed maize led to yield decrease on drylands by 32% of potential yield on the average in Pleven, by 20% in Lom and Silistra and by 10% in Varna thus indicating that innovative risk approaches are required.
Keywords: Chernozems; maize crop season; North Bulgaria; risk assessment of climate change
Date published: 2017-02-13
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