Drought Monitoring in Mainland Portugal

Transcription

1 Drought Monitoring in Mainland Portugal 1. Accumulated precipitation since 1st October 2014 (Hydrological Year) The accumulated precipitation amount since 1 October 2014 until the end of April 2015 (Figure 1) is below the normal values ( ) in almost the whole territory. In the last 5 months (from December till April), the precipitation amounts have always been below normal, especially in the months of December, February and March (Figure 2). Figure 1 Accumulated precipitation and percentages of precipitation from 1 October 2014 to 30 April Figure 2 - Monthly precipitation between December 2014 and April 2015 and respective normal values Instituto Português do Mar e da Atmosfera, I.P. 1 6

2 2. Monitoring Meteorological Drought with PDSI In Portugal the Palmer Drought Severity Index, PDSI, is the Index used to detect, characterize and monitor the drought events, detecting the drought periods and classifying them by the intensity. Figure 3 shows the PDSI spatial distribution in January, February and March The drought situation began on February and by the end of March the whole territory was in a meteorological drought situation. Figure 3 PDSI spatial distribution in January, February and March In the first 16 days of April there was an increase in the intensity of the meteorological drought in Northern and Centre regions, especially in the most severe drought classes (severe and extreme), this situation was due to low precipitation values recorded in that period. In the last 15 days of April occurred precipitation which led to a slightly decrease in drought intensity. Figure 4 - PDSI spatial distribution in April (left, 16 april; right, 30 april) Instituto Português do Mar e da Atmosfera, I.P. 2 6

3 Table 1 shows the percentage of the affected territory in the drought classes of PDSI from February, 28 to April, 30. Table 1 Percentage of territory affected by drought Classes PDSI 28 February March April April 2015 Extremely wet Very wet Moderately wet Slightly wet Normal Mild drought Moderate drought Severe drought Extreme drought Monitoring Meteorological Drought with SPI The SPI can be computed for different time scales, which can help in providing warnings of drought and assess to drought severity. Figure 5 shows the evolution of the SPI - 3 months from February to April at the Portuguese main river basins. The 3-month SPI reflects short-and-medium-term moisture conditions and provides a seasonal estimation of precipitation. In this period from December to April it can be observed dry conditions in all basins which reflect a deficiency in the seasonal precipitation, especially in the winter period. December to February (winter) January to March February to April Figure 5 SPI-3 spatial distribution from February to April 2015 Instituto Português do Mar e da Atmosfera, I.P. 3 6

4 Figure 6 shows the SPI - 6 months. This scale indicates the medium-term trends in precipitation. It can be seen that in the winter and early spring period, there s already a sign of drought in some basins of Northern and Center regions. October to March November to April Figure 6 SPI spatial distribution from October 2014 to April 2015 Figure 7 shows the SPI - 12 months. These time scales are tied to streamflows, reservoir levels and groundwater levels and at these level there isn t any sign of drought in Portugal. Figure 7 SPI spatial distribution from March 2014 to April 2015 Instituto Português do Mar e da Atmosfera, I.P. 4 6

5 4. Drought Evolution Scenarios for the end of May 2015 Based on the estimation of PDSI index for three different scenarios of occurrence of the amount of precipitation (decil 2, 5 and 8), the evolution of drought at the end of May, taking into account the situation at the end of April 2015, is presented in Figure 8. Scenario 1 Scenario 2 Scenario 3 Figure 8 Spatial distribution of meteorological drought index on May 31, 2015, for 3 different scenarios of occurrence of the amount of precipitation Scenario 1 (2º decil - D2) - Values of precipitation well below the mean would increase the intensity of drought, especially with a significant increase in severe drought. Scenario (5º decil D5) Values of precipitation near the mean, would lead to an identical situation of April 30, Scenario 3 (8º decil D8) Values of precipitation well above the mean would lead to a significant decrease in the intensity of the drought, but drought will remain in almost the whole territory. Instituto Português do Mar e da Atmosfera, I.P. 5 6

6 5. Temperature After a 2014/15 cold winter in Portugal, the beginning of spring recorded mean temperature values above the normal, especially in the month of April. The mean average air temperature in April was the 3 rd highest in the last 18 years. In the early days of this month there was a warm period, with high values of maximum air temperature and the occurrence of a heat wave from March, 27 to April, 7 (Figure 9). Figure 9 Heat wave from March, 27 to April, 7 in Portugal IPMA forecast for the next 10 days indicates a period with above normal temperatures and dry situation. Instituto Português do Mar e da Atmosfera, I.P. 6 6