Victor Velasco

Historical Droughts in Central Mexico and Their Relation with El Niño

A catalog containing an unprecedented amount of historical data in central Mexico, covering almost six centuries (1450–1900), is used. This is a catalog of agricultural disasters that includes events associated with hydrometeorological phenomena, or hazards, whose effects were mainly felt in the agricultural sector, such as droughts. An analysis of the historical series of droughts in central Mexico for the period of 1450–1900 is performed. Periods of frequent drought centered at the years 1483, 1533, 1571, 1601, 1650, 1691, 1730, 1783, 1818, and 1860 have been identified. In particular, droughts in Mexico City and northwest Mexico that were identified through poor tree-ring growth are included in the frequent drought periods obtained in this work. Moreover, it was found that droughts occurred in El Nino years mainly for events of very strong and strong strengths, at a significant level. Also, most droughts lasted for 1 or 2 yr. Last, by analyzing the periodicities of the drought time series it was found that those that are the most conspicuous are the quasi-bidecadal frequencies of 18.9 and 21 yr.

A study of historical droughts in southeastern Mexico

Abstract A catalog containing an unprecedented amount of historical data in the southeastern part of Mexico covering almost four centuries (1502–1899) is used to construct a drought time series. The catalog records information of agricultural disasters and includes events associated with hydrometeorological phenomena or hazards whose effects were mainly felt in the agricultural sector, such as droughts. An analysis of the historical series of droughts in southeastern Mexico for the period 1502–1899 is performed. The highest drought frequency occurred around the years 1650, 1782, and 1884; no droughts were reported around 1540, between 1630 and 1640, along the largest time lapse of 1672–1714, and between 1740 and 1760. From 1760 until the end of the period of study droughts definitively occur more often than they did from ∼1550 to 1760. In addition, most droughts lasted for 1–2 yr. Analyzing the frequencies of the drought time series it is found that the most conspicuous cycles are ∼3–4 and 7 yr, although ...

A 14.7 Ka record of earth surface processes from the arid-monsoon transitional zone of China

The stability of Earths critical zone is intimately linked with erosion, weathering and vegetation type and density. Therefore, it affects global biogeochemical processes which in turn affect the global climate by absorbing and reflecting solar radiation, and by altering fluxes of heat, water vapour, carbon dioxide and other trace gases through various feedback mechanisms. However, there is a lack of knowledge about how Earths critical zone processes have changed over time and their link with past monsoon variability, especially in Asia. The study of lake sediments, which contain a suite of inorganic elemental and isotopic proxies, may facilitate the understanding of the Earths critical zone processes on millennial timescales. Here we reconstruct the history of erosion-weathering-vegetation interactions since similar to 14.7 ka using geochemical records from a radiocarbon-dated sediment core from Lake Gonghai in the monsoon-arid transitional zone of north China. Detrital (Al, Ti, K, Rb) and authigenic (Ca, Sr) elemental records reveal distinct, millennial-scale, late deglacial-Holocene erosion and weathering patterns and transitions with the former (latter) elements showing higher (lower) values in warm intervals and vice versa. Chemical Index of Alteration (CIA) molar, a humidity proxy, suggests low humidity during the late deglacial similar to 11.5-14.7 ka, high humidity during the early-mid Holocene similar to 11.5-3.2 ka, and intermediate humidity during the late Holocene interval since similar to 3.2 ka. The results of cross-spectral analysis and comparison of our records with other climate reconstructions also suggest a pattern of orbitally-phased humidity changes in north China. Overall, our results provide evidence for the solar-forcing of Earths surface processes in mid-latitude China under natural climatic conditions. Copyright (C) 2017 John Wiley & Sons, Ltd.