Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Master → Etats Unis → 1991 → Effect of weather variation on economic results from grasshopper control tactics in Chad : a partial validation of GHLSIM

Oregon State University (1991)

Effect of weather variation on economic results from grasshopper control tactics in Chad : a partial validation of GHLSIM

Sheikh, Allah Ditta

Titre : Effect of weather variation on economic results from grasshopper control tactics in Chad : a partial validation of GHLSIM

Auteur : Sheikh, Allah Ditta

Université de soutenance : Oregon State University

Grade : Master of Science in Agricultural and Resource Economics 1991

Agricultural production in the Sahelian region of Africa is among the lowest in the world. Cyclical infestations of locusts and grasshoppers have contributed to this low productivity. The infestations appear to be triggered by heavy rainfall at the beginning of a crop season after extended drought. Because locusts and grasshoppers are migratory, their control on a local and farm by farm basis is difficult. To combat the problem of periodic outbreaks USAID has provided direct assistance through aerial spraying of grasshoppers in a number of African countries.’ This includes a control program in the north African country of Chad in 1987. From the beginning concern arose as to when it is economically desirable to control grasshoppers. The International Plant Protection Center (IPPC) at Oregon State University was awarded a contract for economic evaluation of spraying in Chad which included development of a grasshopper crop loss simulation model (GHLSIM) driven by climatic factors for grasshopper and crop growth. GHLSIM’s posterior analysis of the 1987 anti-grasshopper campaign produced results with a wide range of B/C ratios across the 13 sites which were evaluated. The B/C ratios ranged from 0 to 6.9. To test GHLSIM’s use beyond weather conditions of a single year (1987), a Monte Carlo simulation technique was used to generate long term (100 year) rainfall patterns at selected sites and a series of expected benefits generated. The effect of rainfall variability upon economic benefits was assessed. So also were changes in grasshopper population densities and output prices. Results are presented graphically under a number of such conditions to understand the biophysical relationships among grasshoppers, crop, natural vegetation and rainfall as modeled by GHLSIM. The model is sensitive to within season and to some extent between season weather variation. Rainfall appears to be the dominant variable controlling crop production, regardless of grasshopper densities. When weather is the overriding factor, changes in grasshopper density levels do not play a dominant role in affecting B/C ratios. When weather is not a constraint for crop production, grasshopper density changes can affect benefits significantly. In its present form the GHLSIM model cannot be used as an early warning indicator. While the model appears to predict crop production quite well, model refinement which will change the qualitative prediction of grasshopper populations to a quantitative one throughout a crop season is still needed. When this is completed and both the GHLCROPS and GHLOSE submodels performance are validated against field observations, the GHLSIM model can be used as an early warning predictor. With these accomplishments GHLSIM can then be considered for use in the public policy arena for assessing what areas to spray, when and what distributional effects may be involved.

Mots-clés : Grasshoppers — Control — Economic aspects — Chad — Crops and climate — Crop losses — Aerial spraying and dusting in agriculture


Version intégrale (1,58 MB)

Page publiée le 9 mai 2011, mise à jour le 22 février 2018