8. Maya 旱灾
To understand the ancient Mayan people who lived in the area that is today southern Mexico and Central America and the ecological difficulties they faced, one must first consider their environment, which we think of as jungle or tropical rainforest. This view is inaccurate, and the reason proves to be important. Properly speaking, tropical rainforests grow in high-rainfall equatorial areas that remain wet or humid all year round. But the Maya homeland lies more than sixteen hundred kilometers from the equator, at latitudes 17 to 22 degrees north, in a habitat termed a seasonal tropical forest. That is, while there does tend to be a rainy season from May to October, there is also a dry season from January through April. If one focuses on the wet months, one calls the Maya homeland a seasonal tropical forest; if one focuses on the dry months, one could instead describe it as a seasonal desert.
From north to south in the Yucatan Peninsula, where the Maya lived, rainfall ranges from 18 to 100 inches per year, and the soils become thicker, so that the southern peninsula was agriculturally more productive and supported denser populations. But rainfall in the Maya homeland is unpredictably variable between years; some recent years have had three or four times more rain than other years. As a result, modern farmers attempting to grow corn in the ancient Maya homelands have faced frequent crop failures, especially in the north. The ancient Maya were presumably more experienced and did better, but nevertheless they too must have faced risks of crop failures from droughts and hurricanes.
Although southem Maya areas received more rainfall than northern areas, problems of water were paradoxically more severe in the wet south. While that made things hard for ancient Maya living in the south, it has also made things hard for modem archaeologists who have difficulty understanding why ancient droughts caused bigger problems in the wet south than in the dry north. The likely explanation is that an area of underground freshwater underlies the Yucatan Peninsula, but surface elevation increases from north to south, so that as one moves south the land surface lies increasingly higher above the water table. In the northern peninsula the elevation is sufficiently low that the ancient Maya were able to reach the water table at deep sinkholes called cenotes, or at deep caves. In low-elevation north coastal areas without sinkholes, the Maya would have been able to get down to the water table by digging wells up to 75 feet deep. But much of the south lies too high above the water table for cenotes or wells to reach down to it. Making matters worse, most of the Yucatan Peninsula consists of karst, a porous sponge-like limestone terrain where rain runs straight into the ground and where little or no surface water remains available.
How did those dense southern Maya populations deal with the resulting water problem? It initially surprises us that many of their cities were not built next to the rivers but instead on high terrain in rolling uplands. The explanation is that the Maya excavated depressions, or modified natural depressions, and then plugged up leaks in the karst by plastering the bottoms of the depressions in order to create reservoirs, which collected rain from large plastered catchment basins and stored it for use in the dry season.For example, reservoirs at the Maya city of Tikal held enough water to meet the drinking water needs of about 10,000 people for a period of 18 months. At the city of Coba the Maya built dikes around a lake in order to raise its level and make their water supply more reliable. But the inhabitants of Tikal and other cities dependent on reservoirs for drinking water would still have been in deep trouble if 18 months passed without rain in a prolonged drought. A shorter drought in which they exhausted their stored food supplies might already have gotten them in deep trouble, because growing crops required rain rather than reservoirs.
大学英语四级词汇m
赵丽教你巧记英语单词LESSON 81
星火英语2008年6月版听力强攻第1课
赵丽教你巧记英语单词LESSON 1
赵丽教你巧记英语单词LESSON 9
大学英语四级词汇c
赵丽教你巧记英语单词LESSON 27
闭着眼睛飘单词四级notion- occupation
星火英语点评历年四级真题2007年6月四级真题
2008年6月四级预测卷听力(星火)第5课
赵丽教你巧记英语单词LESSON 17
大学英语四级词汇d
2008年6月四级预测卷听力(星火)第3课
赵丽教你巧记英语单词LESSON 24
大学英语四级词汇q
赵丽教你巧记英语单词LESSON 29
赵丽教你巧记英语单词LESSON 108
闭着眼睛飘单词四级penalty- pillar
背1遍就想上考场四级单词74
新四级听力听写练习第四单元lesson18
赵丽教你巧记英语单词LESSON 52
大学英语四级词汇r
大学英语四级考试写作冲刺 01段落
赵丽教你巧记英语单词LESSON 51
赵丽教你巧记英语单词LESSON 39
背1遍就想上考场四级单词 Week 3 Day 2_90
CET4淘金式英语词汇(四级)第1课
cet4英语词汇全攻略第6课
大学英语四级词汇u
大学英语四级考试(CET4)历年真题听力2010年12月英语四级真题听力
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |