Information on the rate and pattern of urban expansion is required by urban planners to devise proper urban planning and management policy directions. This study evaluated the dynamics and spatial pattern of Mekelle City's expansion in the past three decades . Multi-temporal Landsat images and Maximum Likelihood Classifier were used to produce decadal land use/land cover (LULC) maps. Changes in LULC and spatial pattern of urban expansion were analysed by post-classification change detection and spatial metrics, respectively. The results showed that in the periods 1984-1994, 1994-2004, and 2004-2014, the built-up area increased annually by 10%, 9%, and 8%, respectively; with an average annual increment of 19% (100 ha year −1 ), from 531 ha in 1984 to 3524 ha in 2014. Between 1984 and 2014, about 88% of the gain in built-up area was from conversion of agricultural lands, which decreased by 39%. Extension of existing urban areas was the dominant growth type, which accounted for 54%, 75%, and 81% of the total new development during 1984-1994, 1994-2004, and 2004-2014, respectively. The spatial metrics analyses revealed urban sprawl, with increased heterogeneity and gradual dispersion in the outskirts of the city. The per capita land consumption rate (ha per person) increased from 0.009 in 1984 to 0.014 in 2014, indicating low density urban growth. Based on the prediction result, the current (2014) built-up area will double by 2035, and this is likely to have multiple socioeconomic and environmental consequences unless sustainable urban planning and development policies are devised.

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Abstract:Weed competition is one of the most important production constraints causing up to 91.6% reduction in potential yield of cowpea. Therefore, an experiment was conducted at Sirinka and at Jari, northern Ethiopia, during the 2014 main cropping season: to evaluate the effect of planting pattern and frequency of weeding on weeds, yield components and yield of cowpea. There were 18 treatments comprising combination of three planting patterns (S1: 60 cm x 10 cm, S2: 45 cm x 15 cm, S3: 45 cm x 10 cm) and six weeding frequencies viz. one hand weeding and hoeing at 2 weeks after crop emergence (WAE), one hand weeding and hoeing at 3 WAE, one hand weeding and hoeing at 4 WAE, two hand weeding and hoeing at 2 and 5 WAE, weed free check, and weedy check. The treatments were arranged in factorial combination in a randomized complete block design with three replications. Results showed significantly lower total weed dry weight at Sirinka than at Jari. The highest weed control efficacy was recorded in two hand weeding and hoeing at 2 and 5 WAE of cowpea at Sirinka. The plants in weedy check plots at Jari attained maximum height which was significantly higher than all the other treatments. Significantly highest number of pods per plant was recorded in weed free check under 60 cm x 10 cm spacing at Jari. Number of seeds per pod was highest in weed free check at 45 cm x 10 cm spacing at Sirinka. The interaction of weeding frequency and location had significant effect on cowpea dry biomass yield. The highest total dry biomass (12413 kg ha -1 ) was obtained in one hand weeding and hoeing at 4 WAE at Jari while the highest grain yield (4508 kg ha -1 ) was recorded from complete weed free under 60 cm x 10 cm spacing at Sirinka. The harvest index ranged from 18.2% in weedy check at Jari to 39.1% in weed free check at Sirinka. The results indicated that the use of 60 cm x 10 cm planting pattern in combination with hand weeding and hoeing at 3 WAE at Sirinka and hand weeding and hoeing at 4 WAE at Jari proved to be the most feasible practice.