Marked interannual fluctuations in rainfall are a fundamental aspect of southern African climate. This study uses dry spell frequency (DSF) to assess spatial and temporal patterns in the consistency of rainfall during the mid-summer (DJF) season and their relationships to interannual drought occurrences in southern Africa. The Climate Prediction Center Merged Analysis of Precipitation (CMAP) pentad data are used to identify dry spells, which are defined here as a pentad with mean daily rainfall less than 1 mm. It was found that DSFs over most of southern Africa are highest (lowest) during El Niño (La Niña) events and that their occurrence is associated with shifts in the location of the tropical-temperate-trough (TTT) systems that are the dominant rain-producing systems over much of southern Africa. The latter are tropical-extratropical cloudbands that link a tropical low over low latitude southern Africa with a westerly disturbance passing south of the landmass. A preferred zone of occurrence of high DSFs, within which the interannual range is also highest, lies across the 20 to 25°S band in southern Africa and is identified as the drought corridor. This region often experiences half or more of the season under dry spells. In addition, a tendency during 1979 to 2002 towards an increasing frequency of heavier rainfall events was observed over Angola/Namibia in the west and Tanzania/Mozambique in the east. Only a small area in central southern Africa showed the reverse tendency. 26: 199-211, 2004 troughs (TTTs) play in determining the nature of the summer season over southern Africa. TTTs are tropical-extratropical cloudbands that link a tropical low over low-latitude southern Africa with a westerly disturbance passing south of the landmass. Typically, the bands line up NW-SE across subtropical southern Africa, with a significant polewards export of moisture and heat, and good rainfall in the vicinity of this synoptic system. In some seasons, the TTTs tend to be located further east when the tropical source is over the eastern margins of the sub-continent or even Madagascar. If this is the case, then most of southern Africa tends to experience significantly reduced rainfall. KEY WORDS: Dry spell frequency · Southern Africa · ENSO Resale or republication not permitted without written consent of the publisherClim ResThe earlier studies of and Tennant & Hewitson (2002) were limited in temporal coverage and to South Africa, respectively. Thus, there is room for additional studies over the entire subcontinent south of the equator that use now available merged (rain gauge and satellite-derived) rainfall data.Applications of rainfall variability studies to many fields such as agriculture and water resource management need more detailed information than just departures from a 'mean' state. For example, it is known that a season with above-average rainfall over an agricultural region may not be any better than a belowaverage season if the rains are not well distributed in either time or space. For crop culti...

Subsistence farmers within southern Africa have identified the onset of the maize growing season as an important seasonal characteristic, advance knowledge of which would aid preparations for the planting of rain-fed maize. Onset over South Africa and Zimbabwe is calculated using rainfall data from the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the Computing Center for Water Research (CCWR). The two datasets present similar estimates of the mean, standard deviation, and trend of onset for the common period (1979–97) over South Africa. During this period, onset has been tending to occur later in the season, in particular over the coastal regions and the Limpopo valley. However, the CCWR data (1950–97) indicate that this is part of long-term (decadal) variability. Characteristic rainfall patterns associated with late and early onset are estimated using a self-organizing map (SOM). Late onset is associated with heavier rainfall over the subcontinent. When onset is early over Zimbabwe, there is an increased frequency of more intense rainfall over northeast Madagascar during the preceding August. Accompanying these intense events is an increased frequency of positive 500-hPa geopotential height anomalies to the southeast of the continent. Similar positive height anomalies are also frequently present during early onset. The study indicates that onset variability is partly forced by synoptic conditions, and the successful use of general circulation models to estimate onset will depend on their simulation of the zonally asymmetric component of the westerly circulation.

Detailed analysis of Land Use/Land Cover (LULC) using remote sensing data in complex irrigated basins provides complete profile for better water resource management and planning. Using remote sensing data, this study provides detailed land use maps of the Lower Chenab Canal irrigated region of Pakistan from 2005 to 2012 for LULC change detection. Major crop types are demarcated by identifying temporal profiles of NDVI using MODIS 250 m  250 m spatial resolution data. Wheat and rice are found to be major crops in rabi and kharif seasons, respectively. Accuracy assessment of prepared maps is performed using three different techniques: error matrix approach, comparison with ancillary data and with previous study. Producer and user accuracies for each class are calculated along with kappa coefficients (K). The average overall accuracies for rabi and kharif are 82.83% and 78.21%, respectively. Producer and user accuracies for individual class range respectively between 72.5% to 77% and 70.1% to 84.3% for rabi and 76.6% to 90.2% and 72% to 84.7% for kharif. The K values range between 0.66 to 0.77 for rabi with average of 0.73, and from 0.69 to 0.74 with average of 0.71 for kharif. LULC change detection indicates that wheat and rice have less volatility of change in comparison with both rabi and kharif fodders. Transformation between cotton and rice is less common due to their completely different cropping conditions. Results of spatial and temporal LULC distributions and their seasonal variations provide useful insights for establishing realistic LULC scenarios for hydrological studies.

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