500-yr. precipitation variability in Southern Taihang Mountains, China, and its linkages to ENSO and PDO

Bao

et al. 2019

Forests

Water source is one of the most important concerns for regional society and economy development, especially in the Weihe River basin which is located in the marginal zone of the Asian summer monsoon. Due to the weakness of short instrumental records, the variations of streamflow during the long-term natural background are difficult to access. Herein, the average June–July streamflow variability in the middle reaches of the Weihe River was identified based on tree-ring width indices of Chines pine (Pinus tabulaeformis Carr.) from the northern slope of the Qinling Mountains in central China. Our model could explain the variance of 39.3% in the observed streamflow period from 1940 to 1970 AD. There were 30 extremely low years and 26 high years which occurred in our reconstruction for the effective span of 1820 to 2005. Several common dryness and wetness periods appeared in this reconstructed streamflow, and other tree-ring precipitation series suggested the coherence of hydroclimate fluctuation over the Weihe River basin. Some significant peaks in cycles implied the linkages of natural forcing on the average June–July streamflow of the Weihe River, such as the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) activities. Spatial correlation results between streamflow and sea surface temperature in the northern Pacific Ocean, as well as extremely low/high years responding to the El Niño/La Nina events, supported the teleconnections. The current 186-year streamflow reconstruction placed regional twentieth-century drought and moisture events in a long-term perspective in the Weihe River basin, and provided useful information for regional water resource safety and forest management, particularly under climate warming conditions.

Section: Variation Features Of Streamflow Of the Weihe Riversupporting

confidence: 56%

Two Centuries-Long Streamflow Reconstruction Inferred from Tree Rings for the Middle Reaches of the Weihe River in Central China

Bao

et al. 2019

Forests

“…Twelve El Niño events occurring in the reconstructed drought index series accounted for 38.71% of the extreme dry years, while nine La Niña events accounted for 31.03% of the extreme wet years. Similar cycles related to ENSO have been revealed in other tree-ring climate variable reconstruction series in surrounding regions [11,15,16,34,51,52].…”

Section: Regional Drought Signals and Teleconnectionsupporting

confidence: 77%

Response Characteristics of Chinese Pine (Pinus tabulaeformis Carr.) Radial Growth to Climate and Drought Variability Reconstruction in Western Liaoning, Northeast China

Bao

Bao³

2019

Forests

Chinese pine (Pinus tabulaeformis Carr.) plays an important role in maintaining ecosystem health and stability in western Liaoning Province and the southern Horqin sand land, Northeast China, with benefits including sand fixation and soil erosion. In the context of climate change, developing a better understanding of the relationship between climate factors and growth rates of this species will be extremely valuable in guiding management activities and meeting regional conservation objectives. Here, the results based on two groups of tree-ring samples show that the radial growth of Chinese pine is controlled primarily by water conditions. The longer chronology had the highest correlation coefficient with the January-September mean self-calibrating Palmer Drought Severity Index (scPDSI); therefore, drought variability was reconstructed for the period 1859-2014. Statistical analysis showed that our model explained 41.9% of the variance in radial growth during the 1951-2014 calibration period. Extreme dry and wet events, defined as the criteria of one standard deviation less or greater than the mean value, accounted for 19.9% and 18.6% of the 156-year climate record, respectively. During the past century, the regional hydroclimate experienced significant long-term fluctuations. The dry periods occurred from the early-1900s-1930s and 1980s-2000s, and the wet periods occurred from the 1940s-1970s. The drought reconstruction was consistent with the decreasing trend of the East Asian summer monsoon since the late 1970s. The reconstructed temporal patterns in hydroclimate in western Liaoning were closely related to the large-scale climate drivers in the North Pacific and the tropical equatorial Pacific. The teleconnections were confirmed by spatial correlations between the reconstructed sequence and sea surface temperature (SST) in the North Pacific, as well as the correlations with the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO) indices. Aerosols played an important role in affecting drought variations over the past several decades. Moisture stress caused by global warming and interdecadal changes in the PDO will have long-term effects on the growth of pines in the study area in the future.

“…Considering the TRW series of P. tabuliformis in Baiyunshan and Longchiman are mainly restricted by the early summer moisture conditions, we hypothesize that the early summer hydroclimatic signals might be strengthened only using EWW, since earlywood is mostly formed before mid-July (Zhang et al, 1982). Therefore, the objectives of this study are (1) to verify that EWW is more sensitive to early summer hydroclimatic factors than TRW and LWW for P. tabuliformis at Baiyunshan and Longchiman, (2) to reconstruct early summer hydroclimate variations using EWW, and (3) to tentatively explore the relationship between the reconstructed hydroclimate variability and EASMI.…”

Section: Introductionmentioning

confidence: 98%

Early summer hydroclimatic signals are captured well by tree-ring earlywood width in the eastern Qinling Mountains, central China

Zhao¹,

Shi²,

Shi³

et al. 2019

Clim. Past

Abstract. In the humid and semi-humid regions of China, tree-ring-width (TRW) chronologies offer limited moisture-related climatic information. To gather additional climatic information, it would be interesting to explore the potential of the intra-annul tree-ring-width indices (i.e., the earlywood width, EWW, and latewood width, LWW). To achieve this purpose, TRW, EWW, and LWW were measured from the tree-ring samples of Pinus tabuliformis originating from the semi-humid eastern Qinling Mountains, central China. Standard (STD) and signal-free (SSF) chronologies of all parameters were created using these detrending methods including (1) negative exponential functions combined with linear regression with negative (or zero) slope (NELR), (2) cubic smoothing splines with a 50 % frequency cutoff at 67 % of the series length (SP67), and (3) age-dependent splines with an initial stiffness of 50 years (SPA50). The results showed that EWW chronologies were significantly negatively correlated with temperature but positively correlated with precipitation and soil moisture conditions during the current early-growing season. By contrast, LWW and TRW chronologies had weaker relationships with these climatic factors. The strongest climatic signal was detected for the EWW STD chronology detrended with the NELR method, explaining 50 % of the variance in the May–July self-calibrated Palmer Drought Severity Index (MJJ scPDSI) during the instrumental period 1953–2005. Based on this relationship, the MJJ scPDSI was reconstructed back to 1868 using a linear regression function. The reconstruction was validated by comparison with other hydroclimatic reconstructions and historical document records from adjacent regions. Our results highlight the potential of intra-annual tree-ring indices for reconstructing seasonal hydroclimatic variations in humid and semi-humid regions of China. Furthermore, our reconstruction exhibits a strong in-phase relationship with a newly proposed East Asian summer monsoon index (EASMI) before the 1940s on the decadal and longer timescales, which may be due to the positive response of the local precipitation to EASMI. Nonetheless, the cause for the weakened relationship after the 1940s is complex, and cannot be solely attributed to the changing impacts of precipitation and temperature.