However, a shortage of rainfall does not necessarily mean a drought will occur. Sometimes, if a shortage of rainfall happens in cooler conditions, water evaporation from the soil slows down and plants have an easier time retaining moisture in the soil rather than returning it to the air (via transpiration). However, in warmer conditions, evapotranspiration (the total amount of water returned to the air by either evaporation or transpiration) increases, and dry conditions can develop faster and more easily. Environmental factors like climate change, ocean temperatures, changes in the jet stream, and changes in the local landscape all make a difference when it comes to droughts.
Droughts are particularly dangerous for people living in areas without enough food or water, or who are income or nutrition-dependent on what they grow. If crops fail and livestock die, there is not enough food to go around and malnutrition and drought-related diseases rapidly increase. Moreover, when a region is very poor and does not have enough food or water, arguments can happen over who should be able to access the goods, which can even escalate into larger scale conflict, with researchers linking the intensification of the Syrian conflict to a drought caused by climate change [NY Times].
From 1970 to 2012, drought caused almost 680 000 deaths [World Meteorological Organization].