Study of an Apennines river hydrological data since 1959. Streamflow and relation to land cover dynamic and rainfall change.

Study of an Apennines river hydrological data since 1959. Streamflow and relation to land cover dynamic and rainfall change. A. Ghermandi*, C. Cavazza**, L. Canciani*** and D. Pavanelli**** * School of Agriculture and Veterinary Medicine, University of Bologna, Bologna, Italy ** Reno Catchment Technical Service, Emilia-Romagna Region, Bologna, Italy *** Reno Catchment Authority, Emilia-Romagna Region, Bologna, Italy **** Department of Agricultural and Food Sciences, University of Bologna, Bologna, Italy (E-mail: donatella.pavanelli@unibo.it) The aims of this paper were to study the River Samoggia hydraulic regime trend occurred between 1959 and 2014, the connection between flow variations (Q), rainfall (P) trends and the land use dynamics on the mountain basin (agricolture and forest practices) The Samoggia is a typical torrent in Emilian Apennines, Northern Italy; it is 62 km long with 457 km 2 catchment surface. The Samoggia catchment is located within the Apennine climatic zone, characterized by two periods of maximum P, in autumn and spring, and one period of minimum P in summer. The T mean is 10,7 °C, the mean July T max is 24,7 °C. The bedrock of its catchment consists of relatively easily erodible clays in the upstream and weakly cemented sandstone in the downstream. It is classified as an almost impermeable basin. The basin as a low elevation: the highest and mean altitudes are 875 m and 374 m a.s.l. respectively. Because of its low elevation, hills and valley are intensely cultivated and inhabited: agricultural areas represent the 54% of the entire surface, mostly are arable lands, but there are orchards and vineyards too. Mean streamflow data, collected at the Calcara gauge (44°32’50’’ North, 11°8’0,2’’ East), the conventional mountain catchment ends, and annual rainfall data, collected in nine gauge stations of the basin, between 1959 and 2014, were analysed. All the data were collected by Italian Hydrographic Service (SIMN) and Emilia-Romagna Regional Agency for Environmental Protection (ARPAE). The land use dynamic of the mountain basin was studied with historical maps and aerial photographs of 1955, 1976 and 2008 years. The uses were categorised according to CORINE Land Cover classification. Results Annual average values of Samoggia basin P and Q are 893 mm and 1.52 m 3 /s respectively, with the characteristics standard deviation of 190 mm and 0.75 m 3 /s. Annual average P and O (Outflow) of catchment decreased in the period 1959-2014 of almost -16% and -40% respectively, referring the mean values of the last ten years (2005-14) to the first ten (1959- 68) of the examined period. This decrease is reflected in the reduction of water bodies, which corresponds to the stream width, from 6% to 1.85%, between 1955 and 2008. The different reduction in inflow and outflow could be due also to the anthropogenic impact on the mountain basin, in addition to the more prevalent climate change. The most significant changes concern artificial areas that increased from 2% to 5.51% in 1955 and 2008 respectively; on the contrary there was the reduction of uncultivated lands from 22% to 10.46%, even so between 1955 and 2008 forests increased from 18% to 28%, cultivated lands remains almost unchanged about 52-54%. The numerous dams built about 1955-60 years are another important factor. In order to obtain a better analysis, the mean monthly hydro-climatic data were split into two groups, 1959-1970 and 1971-2014 (figure 2) the most relevant changes of inflow were in September (-23%), December (-21%) and in the summer months of June-July (16% and 11%) respect to the 1959-2014 average. Instead the outflow reduction is 2-3 times higher and affects all months, except August and September because urban water purifier. The values of the ratios O/P decreases from 0.40 on the first period 1959-1969, to 0.32 (1970 to 1996), to the minimum mean value 0.27 in actual period from 1997 to 2014. The drop of precipitations in the analysed period, combined with the catchment geomorphological configuration and the raised human impact (e.g. increase of irrigation water use), led to a stream flow decrease, which has been gone hand in hand with the increase of anthropic pressure on the basin. This initial hydrological data analysis showed a strong correlation between land use evolution and water discharge at the watershed outlet. Nevertheless, this study shows that the land use is not the only key factor that has to be taken into account when predicting potential future hydrological responses of a watershed. We must consider the type of agriculture, the urbanization, the rainfall season changes and the temperature trend also. Figure 1. Italy and study area: the River Samoggia mountain basin. Figure 2. Monthly inflows and outflows % variations of sub-period 1971-2014 respect 1959-2014 average. Figure 3. The outflows/inflows ratios of the Samoggia catchment decreases. -60 -40 -20 0 20 40 60 jan feb mar apr may jun jul aug sep oct nov dec Percentage OUTFLOW INFLOW 0,00 0,20 0,40 0,60 0,80 1959 1963 1967 1971 1975 1979 1990 1994 1998 2002 2006 2010 2014 Outflows/Inflows