(1)结合上图,分析该区域商周时期与现在气候特征的差异。_____________________________________________________________________________(2)结合所学地理知识,分析该区域水土流失的自然原因。_____________________________________________________________________________(3)根据地理环境整体性原理,分析在水土流失的过程中本区域各地理要素(土壤、地貌、气候、植被、水文)是如何变化的。__________________________________________________________________________________________________________________________________________________________(4)淤地坝是指在各级沟道中,以拦泥淤地为目的而修建的建筑物,修建淤地坝是黄土高原小流域治理的有效方法,简要说明建淤地坝的积极意义。__________________________________________________________________________________________________________________________________________________________