Changes in the intensity and frequency of precipitations are likely to affect the hydrologic cycle much more than changes in the mean climate. In this work, the hypothesis that long term series of short duration maximum annual rainfall are stationary has been evaluated. Values of annual maximum of 1, 3, 6, 12, 24 hours precipitations from 21 weather stations in Friuli Venezia Giulia region were collected for the period 1922‐2009; trend analysis on raw data series was performed using linear regression and Mann‐Kendall test. For each duration and location series, EV‐I distribution was used to calculate the critical values (quantiles) of precipitation according to return periods of 2, 20, and 100 years on moving windows of 20 years including at least 15 useful values; on these data, trend analysis was performed using linear regression and break points were searched using the Pettitt test. Linear regression and Mann‐Kendall test performed on raw data suggested that in most cases the maximum value of short‐duration rainfall increased along time; however, the trend was only seldom statistically significant. On the contrary, regression of 1, 3, 6, and 12 hours precipitations quantiles computed for all return periods showed a significant increase with time, while the opposite was observed for 24h quantiles. Break points were detected in most series, with differences between periods up to 50%. The results indicate that trends of intense rainfall are not univocally defined, therefore suggesting that data for hydrological design must be carefully selected.

Trends in intense precipitations in Friuli Venezia Giulia (NE Italy)

CECCON, Paolo;CAZORZI, Federico
2011-01-01

Abstract

Changes in the intensity and frequency of precipitations are likely to affect the hydrologic cycle much more than changes in the mean climate. In this work, the hypothesis that long term series of short duration maximum annual rainfall are stationary has been evaluated. Values of annual maximum of 1, 3, 6, 12, 24 hours precipitations from 21 weather stations in Friuli Venezia Giulia region were collected for the period 1922‐2009; trend analysis on raw data series was performed using linear regression and Mann‐Kendall test. For each duration and location series, EV‐I distribution was used to calculate the critical values (quantiles) of precipitation according to return periods of 2, 20, and 100 years on moving windows of 20 years including at least 15 useful values; on these data, trend analysis was performed using linear regression and break points were searched using the Pettitt test. Linear regression and Mann‐Kendall test performed on raw data suggested that in most cases the maximum value of short‐duration rainfall increased along time; however, the trend was only seldom statistically significant. On the contrary, regression of 1, 3, 6, and 12 hours precipitations quantiles computed for all return periods showed a significant increase with time, while the opposite was observed for 24h quantiles. Break points were detected in most series, with differences between periods up to 50%. The results indicate that trends of intense rainfall are not univocally defined, therefore suggesting that data for hydrological design must be carefully selected.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11390/870911
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