Abstract: The aim of the research was an agro-climatologic assessment of the amount of rainfall on a local scale, mainly aimed to identify trends in their changes and a possible rise in their variability over time. In the studies also we wanted to demonstrate the impact of the amount of rainfall in the region of Bydgoszcz on the yield of some crops. Material for the study consists of rainfall measurements, carried out in a stand- ard way in the years 1981-2010 at the Research Station of the University of Technology and Life Sciences in Bydgoszcz. Station is located in the village of Mochle, located approximately 20 km from the city centre (φ=53013’ N, λ=17051’E, h=98.5 m above sea level) in sparsely urbanized and industrialized area. We also used data of the yield of selected crops (potato, barley, corn for grain, legumes), from the production in the region of Kujawy and Pomorze as well as from our own experimental field. It has been shown that the average long-term rainfall during the growing season allows for classifying Bydgoszcz region as the area with the lowest rainfall in Poland. Analyzed rainfalls were characterized by a very high variability in time, resulting in climatic risk of plant growing. The largest temporal variability related to August. However, there was no extension of the time variability of rainfall totals in the period 1996-2010, as compared to the period 1981-1995. The sole significant growth trend during the period 1981-2010 was found in May. It appeared a tendency to a decline in summer rainfall totals (VI-VIII) in the annual rainfall total, which is consistent with the IPCC projections. Rainfall totals had highly signi cant impact on yields of selected crops. The highest correlation coefficients were found in relations crop-rainfall in the months of increased water needs of plants. Better correlations rainfall-crop were found using data from the production scale as compared with the scale of experimental field.

Abstract: Climate change suggests long periods without rainfall will occur in the future quite often. Previous approach on dependence crop-yields from size of rain confirms the existence of a statistically significant relation. We built a model describing the amount of precipitation and taking into account periods of drought, using a mixture of gamma distribution and one point-distribution. Parameter estimators were constructed from rainfall data using the method of maximum likelihood. Long series of days or decades of drought allow to determine the probabilities of adverse developments in agriculture as the basis for forecasting crop yields in the future (years 2030, 2050). Forecasted yields can be used for assessment of productivity and profitability of some selected crops in Kujavian-Pomeranian region. Assumptions and parameters of large-scale spatial economic models will be applied to build up relevant solutions. Calculated with this approach output could be useful to expect decrease in agricultural output in the region. It will enable to shape effective agricultural policy to know how to balance food supply and demand through appropriate managing with stored food raw material and/or import/export policies. Used precipitation-yields dependencies method let verify earlier used methodology through comparison of obtained solutions concerning forecasted yields and closed to it uncertainty analysis.This work was co-financed by NCBiR, Contract no. FACCE JPI/04/2012 – P100 PARTNER