Olives tumble with a gentle "plop" onto a tarpaulin in eastern Afghanistan, an unusual, drought-resistant harvest offering hope to farmers who have struggled as climate change worsens water shortages.Drought and water scarcity affect more than half of the country's population, according to the UN, pushing some farmers to seek alternatives to maize, rice or wheat. Abdullah Orzala's olive grove, first planted 15 years ago on his family's land in…