<P> A study published in Science in 2012 found that modest rainfall reductions, amounting to only 25 to 40 percent of annual rainfall, may have been the tipping point to the Maya collapse . Based on samples of lake and cave sediments in the areas surrounding major Maya cities, the researchers were able to determine the amount of annual rainfall in the region . The mild droughts that took place between 800--950 would therefore be enough to rapidly deplete seasonal water supplies in the Yucatán lowlands, where there are no rivers . </P> <P> A study published in Nature Scientific Reports in 2016 showed that between 750 and 900 a cluster of four earthquakes affected the wet tropical mountains south of the Yucatán lowlands, which are not vulnerable to drought, and include such important cities as Quirigua and Copán . These earthquakes left detectable destruction in several Maya cities and led to the abandonment of Quirigua . The study hypothesizes that repeated destruction combined with declining trade with the Maya kingdoms of the Yucatán lowlands to propagate the collapse to the southern part of the Maya realm . </P> <P> LIDAR scanning of the Classic Maya heartlands bolsters the drought theory . A huge population as we now understand existed would not ordinarily disappear from civil war, revolution, soil degradation, disease, earthquake or other suspected factors . Drought, the absence of water in an agricultural system heavily dependent upon water, is almost the only remaining possibility for the collapse in the entire heavily populated region . The Yucatán may have provided underground water and more rainfall to permit the continuance of Mayan civilization there . </P> <P> Some ecological theories of Maya decline focus on the worsening agricultural and resource conditions in the late Classic period . It was originally thought that the majority of Maya agriculture was dependent on a simple slash - and - burn system . Based on this method, the hypothesis of soil exhaustion was advanced by Orator F. Cook in 1921 . Similar soil exhaustion assumptions are associated with erosion, intensive agricultural, and savanna grass competition . </P>

What 3 explanations have been given for the collapse of the maya civilization