Crop and pasture monitoring in Eritrea

Transcription

1 JRC SCIENTIFIC AND POLICY REPORTS Crop and pasture monitoring in Eritrea Kremti rainy season started with substantial delay Ana Pérez-Hoyos, Francois Kayitakire, Hervé Kerdiles, Felix Rembold, Olivier Léo, Josh Hooker August 2013 NDVI anomaly in the 3 rd dekad of July Source: JRC-MARS, SPOT-VGT

2 1. INTRODUCTION Eritrea covers about km 2 of which a significant part in the north and south-east is very dry, hence unsuitable for agriculture. Land use statistics indicate that livestock-related activities make use of 56% of the area whereas cultivated rain fed land covers 5% of the territory. There are typically three rainy seasons: the Azmera between March and May is characterized by short rains that fall mainly in the highlands (Debub and Maekel zones); the Kremti season, between late June and September which usually brings heavy rains to most of Eritrean territory except the coastal lowlands; and the Bahri season (from December to February) that occurs mainly in the eastern lowlands and escarpments (North Red Sea zone). This report provides a rapid assessment of the start of the current Kremti rainy season with special emphasis on the agricultural areas, mainly located in the Debub, Maekel, Gash Barka and Anseba zobas (Figure 1), because this season in Eritrea forms the basis for the main annual cereal harvest. The analyses based on satellite imagery and meteorological data presented in this report show that this crop season was substantially delayed; significant rains for planting arrived only in August in a large part of the country (Gash Barka, Anseba and North Red Sea). Livestock is similarly affected because the early rains in June were not enough to maintain pastures in good conditions. The situation is less critical in the moist highlands (Debub and Maekel) although dry spells were observed also in July in those areas. The dry weather affected not only the crop development but had also an effect on cultivated area. Abundant rains of early August have improved the situation but the negative effect of the delay on this year s harvest will not be completely reversed. Figure 1. Cropland in Eritrea. Source: JRC crop mask (v2.2) 2

3 2. PRECIPITATION ANALYSIS The present Kremti rainy season is characterised by an erratic start in mid-june, a very dry July and very humid August. The first Kremti rains arrived in the highlands (Debub and Maekel zones) in the second dekad of June, giving hope of a normal start of the season in that area. These rains were beneficial for pastures but the quantity that fell in July on those zones was quite below the historical average, so that the planting was delayed. In Gash Barka and Anseba zones, significant rains for crop planting arrived only in August. According to rainfall estimates derived from the operational forecast model of the European Centre for Medium-Range Weather Forecasts (ECMWF), below normal rainfalls were observed in all the western and central parts of Eritrea where are located the main agricultural areas (Figure 2). The 1 st dekad of July was characterised by drier-than-usual conditions over Eritrea. The 1 st dekad received less than 20 mm (around 1-10 mm) for most of the country, a value which is usually taken as an indicative threshold for crop planting (Figure 2). The weather remained drier than expected in the 2 nd dekad of July. Total rainfalls in the 2 nd dekad have been globally below 10 mm in the north-western area of Gash Barka and south of Anseba. The central moist highlands and western moist lowlands areas, mainly part of the Gash Barka zoba, the Debub and Maekel zobas, received 20 to 40 mm of rainfall whereas, on average, those areas receive up to 80 mm. The situation slightly improved during the 3 rd dekad of July but the quantity of rains remained insufficient for a normal crop development. Figure 2 shows that the rain front had a delay of about 20 days moving northwards. Figure 2. Ten-daily rainfall (mm) from July 2013 (top) and the historical average ( ) (bottom). Data source: EC-JRC, based on ECMWF model. 3

4 Figure 3 shows the rainfall anomaly calculated as the difference between total rainfalls received during a period (dekad) and the average of total rainfall received during the same period in the previous years. Areas of concern are in the Gash Barka and Anseba zobas, but also Debub at a less extent. The subzoba of Le elay Gash was the most affected. July anomalies go up to 50 mm of deficit in some areas that receive usually around 80 mm of rainfall. Figure 3. Ten-daily rainfall anomalies (mm) compared to the long term average ( ). Data source: EC-JRC, based on ECMWF model. Heavy rains fell in the first and second dekads of August, causing floods in some areas in Gash Barka. While 2013 is the 3 rd driest year for July total rainfall, the amount of rains received in the 2 dekads of August makes 2013 the wettest year since 1989 in Gash Barka (Figure 4). Although the rainy season has now effectively begun, the delay had an impact on cultivated area. For instance, according to the Ministry of Agriculture, there was plan to cultivate 240 thousand hectares of land in Gash Barka but due to the late coming of the rainfall 150 thousand hectares had been cultivated by mid-august. The delay of rains created also concerns among pastoralists but the situation improved substantially in August. Figure 4. Ranking of 2013 (red) in the last 25 years ( ) based on total July rainfall (left) and total rainfall received in the 1 st and 2 nd dekads of August (right) in Gash Barka zone, Eritrea. 4

5 3. VEGETATION ANALYSIS The July dry spell has had a strong impact on vegetation development, especially in Gash Barka zone, as shown on figure 5. The maps represent the anomalies of the normalized difference vegetation index (NDVI) derived from remote sensing satellite images. The NDVI anomalies in the 1 st dekad of July are small as this is the very beginning of the season. The areas showing positive anomalies in Maekel and Debub are actually areas where the crop season is delayed because in agricultural areas the NDVI reaches the lowest values at the very beginning of the season when fields are ploughed. This is evident on the NDVI temporal profiles of section 4.2 (Figure 6). Vegetation growth is significantly delayed in the agricultural areas located in Gash Barka, Maekel, Debub and South Anseba, with poor and very poor conditions in those main pastoral and grain producing areas. Negative anomalies persisted and even worsened throughout the 3 rd dekad of July, indicating very critical conditions in those areas. Poor conditions are also recorded in the few agricultural places of North Red Sea that produce in this season. Although the vegetation development resumed in August, negative anomalies persisted until the second dekad (Figure 5, bottom). 1 st dekad, Aug nd dekad, Aug 2013 Figure 5. Vegetation conditions (NDVI) in July and August 2013 compared to historical average ( ). Data: SPOT-VGT NDVI 5

6 4. TEMPORAL ANALYSIS OF NDVI AND RAINFALL PROFILES The NDVI and the rainfall time series are analysed together to assess the rainfall temporal distribution and its timing in relation to the vegetation growth stage. Profiles of some agricultural sub-zobas are shown on Figure 6. The vegetation index trend in the moist highlands (Maekel and Debub) show an early vegetation onset, with slightly higher than average NDVI values in June in most sub-zobas. Early planted short-cycle crops are mainly produced in those areas. The vegetation growth rate declined in July due to dry spells but the NDVI values at the end of the month were close to their long-term average. Although this can be seen as normal conditions, there is an effect on the performance of sensitive crops like pulses and vegetables. A different pattern is observed in the south-western lowlands (Gash Barka and Anseba), the second agricultural productive area after the moist highlands, and the north-eastern lowlands where the vegetation merely developed in June and then dried up in July. The vegetation conditions, as assessed from satellite remote sensing data-derived indices, show a significant drop at the end of July. The situation improved in August thanks to abundant rainfall but it remains below the historical average. 4.1 Maekel Figure 6. Profiles of vegetation index (NDVI) and rainfall estimates for the Kremti rainy season for selected, typical sub-zobas. The graphs compare the current season values with their corresponding historical average. 6

7 4.2 Debub Figure 6 (ctd). Profiles of vegetation index (NDVI) and rainfall estimates for the Kremti rainy season for selected, typical sub-zobas. The graphs compare the current season values with their corresponding historical average. 7

8 4.3 Anseba Figure 6 (ctd). Profiles of vegetation index (NDVI) and rainfall estimates for the Kremti rainy season for selected, typical sub-zobas. The graphs compare the current season values with their corresponding historical average. 4.4 Gash Barka 8

9 4.5 North Red Sea Figure 6 (ctd). Profiles of vegetation index (NDVI) and rainfall estimates for the Kremti rainy season for selected, typical sub-zobas. The graphs compare the current season values with their corresponding historical average. 9

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