Due to the Horn of Africa's semi-arid and arid climate, droughts are not uncommon. They are complicated by climate change and changes in agricultural practices. For centuries, the region's pastoral groups have observed careful rangeland management practices to mitigate the effects of drought, such as avoiding overgrazing or setting aside land only for young or ill animals. However, population growth has put pressure on limited land and led to these practices no longer being maintained. Droughts in 1983–85, 1991–92, 1998–99 and 2011 have disrupted periods of gradual growth in herd numbers, leading to a decrease of between 37% and 62% of the cattle population. Initiatives by ECHO and USAID have succeeded in reclaiming hundreds of hectares of pastureland through rangeland management, leading to the establishment of the Dikale Rangeland in 2004.