Drought, agricultural adaptation, and sociopolitical collapse in the Maya Lowlands

Abstract

Paleoclimate records indicate a series of severe droughts was associated with societal collapse of the Classic Maya during the Terminal Classic period (∼800-950 C.E.). Evidence for drought largely derives from the drier, less populated northern Maya Lowlands but does not explain more pronounced and earlier societal disruption in the relatively humid southern Maya Lowlands. Here we apply hydrogen and carbon isotope compositions of plant wax lipids in two lake sediment cores to assess changes in water availability and land use in both the northern and southern Maya lowlands. We show that relatively more intense drying occurred in the southern lowlands than in the northern lowlands during the Terminal Classic period, consistent with earlier and more persistent societal decline in the south. Our results also indicate a period of substantial drying in the southern Maya Lowlands from ∼200 C.E. to 500 C.E., during the Terminal Preclassic and Early Classic periods. Plant wax carbon isotope records indicate a decline in C4 plants in both lake catchments during the Early Classic period, interpreted to reflect a shift from extensive agriculture to intensive, water-conservative maize cultivation that was motivated by a drying climate. Our results imply that agricultural adaptations developed in response to earlier droughts were initially successful, but failed under the more severe droughts of the Terminal Classic period.

Keywords: Maya civilization; climate adaptation; compound-specific isotope analysis; drought; societal collapse.

Fig. 1.

Map of the Maya Lowlands indicating the distribution of annual precipitation (64) and the location of paleoclimate archives discussed in the text. The locations of modern lake sediment and soil samples (Fig. 2) are indicated by diamonds.

Fig. 2.

Scatter plot showing the negative relationship between annual precipitation and δD_wax-corr measured in modern lake sediment and soil samples (Fig. 1). Results from Lake Chichancanab (CH) and Salpeten (SP) are indicated. The black line indicates a linear regression fit to these data, with regression statistics reported at the bottom of the plot. Large squares indicate mean values for each sampling region, with error bars indicating SEM in both δD_wax-corr and annual precipitation. The black error bar indicates the 1σ error for δD_wax-corr values (SI Text). Original δD_wax data from ref. . VSMOW, Vienna Standard Mean Ocean Water.

Fig. 3.

Plant wax (green; left) and terrigenous macrofossil (red; right) age−depth models for (A) Lake Chichancanab and (B) Lake Salpeten. The age probability density of individual radiocarbon analyses is shown. The black lines indicate the best age model based on the weighted mean of 1,000 age model iterations (62). Colored envelopes indicate 95% confidence intervals. Cal, calendar.

Fig. 4.

(A) The δD_wax-corr records from Lakes Chichancanab and Salpeten, fit with a smoothing spline (thicker lines) to highlight centennial-scale trends. Colored envelopes indicate 1σ error in δD_wax-corr values (±7‰) applied to the smoothing spline fits. Horizontal bands indicate the mean δD_wax-corr values for lake surface sediments and soils from three regions within the Maya Lowlands with different mean annual precipitation (Fig. 2); the width of the bands indicates the SEM of regional mean values. (B) The δ¹⁸O records from two speleothems from the northern (Chaac) and southern (Yok I) Maya Lowlands (8, 9) (Fig. 1), plotted on a common scale to highlight differences in the range and amplitude of δ¹⁸O variability for these two records. E, Early; M, Middle; L, Late; T, Terminal; VPDB, Vienna Pee Dee Belemnite.

Fig. 5.

Record of the difference in δD_wax (ΔδD_wax) between Lake Chichancanab and Lake Salpeten, indicating changes in the precipitation gradient between the northern and southern Maya Lowlands. ΔδD_wax is calculated as the difference between smoothing spline curves fit to isotopic data from each lake core (Fig. 3). The gray envelope indicates the propagated 1σ error for ΔδD_wax (±10‰). Modern ΔδD_wax (Fig. 2) is indicated by the dashed line.

Fig. 6.

Coupled plant wax isotope records of hydroclimate and land use change from (A) Lake Chichancanab and (B) Lake Salpeten, alongside (C) estimates of population in the Lake Salpeten catchment (56) and population density in the central portion of the southern Maya Lowlands (57). The δD_wax-corr and δ¹³C_wax records in A and B are fit to a smoothing spline (thicker lines) to highlight centennial-scale trends. Colored envelopes indicate 1σ error applied to the smoothing spline fits for δD_wax-corr (±7‰) and δ¹³C_wax (±0.5‰). Estimates of percent C₄ plants are discussed in SI Text.