DROUGHT IN MAINLAND Ministério da Ciência, Tecnologia e Ensino Superior Instituto de Meteorologia, I. P. Rua C Aeroporto de Lisboa Tel.: (351) 21 844 7000 e-mail:informacoes@meteo.pt 1749-077 Lisboa Portugal Fax: (351) 21 840 2370 URL: http://www.meteo.pt
DROUGHT IN MAINLAND 1. Drought evolution in Mainland Portugal The geography of the mainland Portugal leads to the occurrence of droughts. While drought is a complex process, where meteorological, hydrological, agronomical and other aspects must me considered, it is possible to follow the onset and evolution of drought events through meteorological indices. To characterize drought in Portugal is used the Palmer Index (Palmer, 1965) which was adapted and calibrated to the specific climatic conditions of mainland Portugal. That index performs a parameterized computation of the soil water balance and compares the estimated soil moisture content with its climatological mean A statistical analysis of 4 long climatological series of the PDSI was made for Mainland Portugal. With respect to the change in variability of the PDSI (Figure 1.1), the negative values seem to dominate the last 20 years of the 20th century. The 1980-decade begins with a sudden and large decrease in the PDSI, maintaining a trend for negative values through several years. The values of the PDSI in the cooling period 1946-1975 are less negative than in the warming period (since 1976), suggesting an increased frequency of droughts in the south of Portugal (Pires, 2003). Figure 1.1 Time series of Palmer Drought Severity Index (PDSI) at 4 stations in mainland Portugal The PDSI average was calculated for the last four decades since 1961 (Figure 1.2). An increase in severity is observed especially between February and April, changing from normal conditions to conditions of mild and moderate drought, namely in February and March (Pires, 2003). 1
Figure 1.2 - PDSI average for the last four decades since 1961 to 2000 in Mainland Portugal To observe the evolutions of drought over the country, national maps are produced showing the monthly PDSI distribution, where is possible to determine drought-prone areas and monitor the spatial and temporal evolution of drought across mainland Portugal, which is helpful to delineate potential disaster areas, such as agriculture impacts, giving a better on-farm decision-making. 2. Drought 20/ in Mainland Portugal 20/ hydrological year was initially favorable with respect to precipitation amounts, because October was an extremely rainy month, except in the Southern region where it was dry to normal. Although, next months were classified as dry to extremely dry, which caused a drought period with high intensity. 2
2.1 Drought monthly evolution Figure 2.1 and Table 2.1 shows the monthly evolution of PDSI index regarding the drought area affected in Mainland Portugal. Figure 2.1 - Area (%) affected by drought (Sep 20 - Oct 20) PDSI Table 2.1_ Percentage of Mainland Portugal affected by drought in 20/ out 30 nov dez jan Area affected by drought in % 20/ 28 fev mar moderately wet 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 slightly wet 47 0 0 0 0 0 0 0 0 0 0 0 6 5 5 normal 22 1 0 0 0 0 0 0 0 0 0 0 6 12 11 mild drought 20 47 30 0 0 26 15 4 0 0 0 0 52 81 83 moderate drought 5 47 48 25 23 22 22 28 3 0 0 3 36 2 1 severe drought 1 5 20 53 44 28 20 20 33 27 29 36 0 0 0 extreme drought 0 0 2 22 33 24 43 48 64 73 71 61 0 0 0 30 abr mai 30 jun jul ago 30 set out 30 nov dez The analysis of the figures and the table reveals an aggravation of the drought conditions in winter months, with attenuation in March, due to precipitation occurrence in the Northern and inner regions of the territory. In summer (June, July and August), the least rainy season, which contributes with about 6% for the annual precipitation, the drought situation worsened. In September and due to the precipitation occurred in the first fifteen days, in particular in the Northern and Centre regions there was attenuation in these regions. 3
At the end of the hydrological year (September 30, 20) the whole territory continued in a drought period with severe to extreme intensity. Figure 2.2 shows the number of consecutive months in which the territory was in a severe and extreme drought situation. Figure 2.2 Spatial representation of the consecutive months in severe and extreme drought situation (Period: Oct Sep ) After October 20 there was a significant attenuation of the drought situation in the whole territory, which led to the absence of areas in severe and extreme drought. On December, 20, 84% of the territory still remained in a drought period with moderate to mild intensity. The spatial distribution of PDSI index during 20/20 is represented in Figure 2.3. 4
Oct 30 Nov Dec Jan 28 Feb Mar 30 Apr May 30 Jun Jul Aug 30 Sep Oct 30 Nov Dec Figure 2.3 PDSI Spatial Distribution (Oct -Dec ) 5
2.2 Comparison, on September 30, with other drought periods since 1941 Figure 2.4 shows the percentage of territory in each one of the meteorological drought classifications, according to PDSI index, where the actual values can be compared with the values on September 30 for the drought years of 1945, 1965, 1976, 1981, 1992, 1995 and 1999. However, except for 1945 and 1995 years, the meteorological drought situation had already ended by then. Figures 2.4 and Table 2.2 show the comparison of the current drought with other years affected by drought. They show that a drought event such as the present one is the worst in the last 60 years: 97% in severe and extreme drought in 20; 83% in severe and extreme drought in 1945. Figure 2.4 Other years affected by drought (referred to September 30) Table 2.2_ Percentage of Mainland Portugal affected by drought on September 30 Drought Classification Area affected by drought in % on September 30 (PDSI) 1945 1965 1976 1981 1992 1995 1999 20 extremely wet 0 1 6 0 0 0 6 0 very wet 0 3 13 0 1 0 7 0 moderately wet 0 21 35 3 3 1 50 0 slightly wet 0 23 33 14 17 4 36 0 normal 0 17 4 21 20 6 1 0 mild drought 1 32 6 55 48 44 0 0 moderate drought 16 4 2 5 11 40 0 3 severe drought 50 0 1 2 0 5 0 36 extreme drought 33 0 0 0 0 0 0 61 6
2.3. Social Economical Impacts The social and economical impacts in 20 were mainly associated with the short precipitation that happened all the year. The drought period that had started in the beginning of 20 had a major increase with this precipitation shortage. The effects were very strong in the agriculture, cattle breeding and in the water reserves, especially in the southeast and Northeastern regions. The abnormal drougth situation, together with the very high temperatures in the summer months, gave origin to serious problemens with very large forest fires. 2.3.1 Main drought impacts in the environment and human activities Agriculture and cattle breeding In the Spring/ Summer period the water storage in some of the embankments of the main agriculture areas was not enough for a normal usage; In many reagions the irrigation campaigns were restrited to just some cultures, while in other regions they were completely forbidden; High reduction in the productivity of the seasonal (Autum-Winter) cereals; The reproduction cicle of some cattle species was strongly conditioned; Reduction of the irrigation areas in Spring-Summer season; Large investments for the agriculture industry in the hidraulics areas, in order to create infrastructures to obtain more water; Cost increase of the irrigation systems due to the shortage; In large areas of the country the cattle breeders needed to be supplied with water for the animals; Decrease in the quantity and quality fruit production; Cost increase of the fuels; Significant decrease of in vegetable production of the country. Energy The dry year led to the need for more electric power obtained from fuels to meet the national needs, with the following effects: The increase of the usage of fossil combustion to produce electric power, increasing the price for CO2 emission licenses from 7,00 /t (in January) to the nearly 30 /t as at the end of the year; The capability of electric energy production based on water resources changed from 30% to 40%, in normal conditions, to less than 15% in the dry period. Information from: http://www.inag.pt/inag20/port/divulga/actualidades/seca/relatoriobalanco.pdf 7
Urban Supply The impact on water supply to the populations during the dry period caused the drying out of the water sources and the loss of their annual replenishing capability. The main affected areas were those with small caption systems in small river basins, or small underground reservoirs (Table 2.3 and Figure 2.5). Table 2.3_ Evolution on the population affected direct or indirectly Affected population Period With transported water With cuts/reduction of the supply 1 st half April 14175 213 1 st half May 8395 2635 1 st half June 26500 26781 2 nd half June 23440 25217 1 st half July 260 26350 2 nd half July 548 532 1 st half August 48500 60061 2 nd half August 94372 1000 1 st half September 73097 66127 2 nd half September 69588 39429 2 nd half October 48883 30083 2 nd half November 11921 13354 2 nd half December 10238 13445 Maximum 94372 1000 Figure 2.5 Number of municipalities with a reeiforcement of the transported water suply (blue) or cuts/reduction to household supply (brown) Information from: http://www.inag.pt/inag20/port/divulga/actualidades/seca/relatoriobalanco.pdf 8
Forest Fires The year of 20 was different from the previous one, because the drought conditions started in 20 allowed the starting of forest fires in the first months of 20 (Jan,Feb,Mar). The number of fires was large, even if the burned area was rather small (source:dgrf). In June the meteorological conditions were aggravated and the fires started with stronger intensity, mainly in July and August. Table 2.4 indicates the number of fires and burned area in 20. Table 2.4_ Number of forest Fires and respective burned area (source: DGRF) Number of occurrences Burned area Periods 20 2000 \20 20 Forest Fires mean Total (ha) 2000 \20 mean January 925 158 858 75 February 2.692 421 3.099 388 March 3.228 1.232 6.564 3.979 April 830 907 678 964 May 1.101 969 1.099 798 June 4.178 3.275 15.114 9.549 July 7.179 5.427 60.374 52.539 August 9.670 7.447 202.353 88.500 September 3.541 5.438 19.365 30.5 October 2.353 1.067 15.481 2.353 November 20 426 5 4 December 46 374 237 777 Total 35.763 27.142 325.226 190.289 The drought caused some conditioning in combating forest fires Decrease in the water supply (from swimming pools, small dams, rivers, etc.) normally used in combating forest fires; Increased difficulties in supplying water to aircraft to combat fires due the decrease in water sources; 9