Got Milk Tea? Musings on a Master’s Thesis

By Cari Leland

I wish I could calculate the total amount of English Breakfast tea I consumed over the past year. While working on my thesis, tea drinking was an integral part of the process. There is something about that piping hot beverage that inspires thought, creativity, focus, and hard work. Mongolians might also agree that there is great value in tea. In fact, teatime could almost be considered part of their cultural heritage. No meal is complete without a steamy cup of milk tea – a drink that is not only nutritious, but also a symbol of the warm hospitality that is prevalent in Mongolian culture.

Honestly, I was not much of a tea drinker prior to my summer of fieldwork in Mongolia. I remember one day of fieldwork when Dr. Baatarbileg Nachin, Byamba, Bayra, and I were on the hunt for old trees. Baatar drove us to a ger owned by some folks that he knew well. The hope was that they could show us the way to good sampling sites. The family greeted us with much warmth, as they kindly offered us yogurt biscuits and milk tea. I sat inside the ger –  young children were playing outside, the livestock were grazing happily in the sun, and a partially-logged forest was viewable in the distance. While sipping milk tea in their home, it became abundantly clear why my thesis research could be important.


A significant portion of Mongolia’s economy is based upon the agricultural and livestock sectors (more than a third of their GDP, in fact), and herding, in particular, is an important part of their cultural identity. Therefore, there is concern over how climate change might impact the livelihood of Mongolians. Could the impacts vary spatially? More importantly, how has climate varied spatially over time? Temperatures have generally been increasing over the past few decades, but recent precipitation trends have varied across the country. Precipitation, in general, is a highly ‘local’ phenomenon that varies significantly across the Mongolian landscape. The lack of long-term instrumental records limits our ability to quantify spatial and temporal climatic variability in Mongolia. That’s when tree rings become useful. Annual growth rings allow us to better understand historical variability in climate, and to place recent climate trends in the context of the past several centuries.

The goal of my master’s thesis was to assess hydroclimatic variability across north-central Mongolia using a large network of tree-ring data. Since precipitation is so spatially variable across the country, my goal was to determine if tree-ring data could be used to define hydroclimatic regions (or regions with unique, historical moisture variability). The network consisted of 21 tree-ring sites and three different species (P. sibirica, P. sylvestris, L. sibirica) (see the map below, Fig. 1). Each study site consisted of multiple trees from which core samples were collected. Some of the data were collected over the past two field seasons, while other sites were sampled in the 1990s and early 2000s through the Mongolian American Tree-ring Project (MATRIP). MATRIP is a research collaboration between Mongolian scientists and researchers from Lamont-Doherty Earth Observatory, and their work made my thesis possible.

Fig 1. Map of tree-ring sites. The light gray represents forest cover. LASI = L. sibirica; PISI = P.sibirica; PISY = P. sylvestris.

To keep it short and sweet, I will only discuss some of my most interesting findings. After using a rotated principal component analysis (RPCA), and other crazy statistics, on the network of tree-ring data, I found 4 unique ‘regions’ within the network (Fig.2 ). Cleverly, I called them the Eastern, Western, Northern and Central regions. These regions are outlined in red in the figure below, where large circles represent the tree-ring sites that have similar growth patterns over time. After more statistical analyses, it was apparent that these regions likely represent ‘hydroclimatic regions’. As you can see, each region has its own, distinct variability in hydroclimate over time (Fig.3).

Fig. 2. The four regions. Note that the OGH growth pattern most closely the growth pattern associated with the Central region.

Fig. 3. Growth patterns of each region; a positive PC score represents above-average growth, and a negative PC score represents below-average growth. Variability in growth is likely a reflection of hydroclimatic variability.

Next, I looked at major historical drought and pluvial events across the entire tree-ring network. Pluvials are extended periods of wet conditions – the opposite of droughts. In the next two figures (Figs. 4 and 5), blue colors indicate generally wet conditions, whereas red indicates dry conditions. Figure 4 shows the major drought event associated with each region. Here, it’s obvious that the Eastern and Western regions of the tree-ring network will often have opposite trends. So, for example 1942-1944 (Fig. 4, Top-left) was a major drought in the Eastern region, but it was pretty wet in the Western region. In studying major pluvial events (Fig. 5) – the conditions were pretty wet across the entire network. Some of these results, particularly maps of major drought events, indicate that the Eastern and Western regions of the network are highly unique from one another. This could partly be attributed to topographic differences, as the Western region is located in the Khangai Mountains, whereas the Eastern region is on the leeward side of the Khentii mountains.

Fig. 4. Major drought events. Top-left, 1942-1944 in the Eastern region. Top-right, 1854-1858 in the Western region. Bottom-left, 1822-1825 in the Northern region. Bottom-right, 1928-1930 in the Central region.

Fig. 5. Major pluvial events. Top-left, 1829-1830 in the Eastern region. Top-right, 1916-1917 in the Western region. Bottom-left, 1985-1986 in the Northern region. Bottom-right, 1958-1960 in the Central region.

If you’d like to see more detailed descriptions of my methods, and other cool results from this study, search for my thesis on the following website: However, it will not be available for a few more months. You can also contact me if you would like a copy.

After reading this, I hope you can see how my research highlights the extent of spatial and temporal variability in hydroclimate across north-central Mongolia. These results could be used to understand regional trends in climate and to potentially help guide water resource management efforts. Recent severe droughts across Mongolia suggest that water management will be increasingly important in coming decades. These findings are an important stepping stone for further research and will be valuable for producing additional climate reconstructions.

The next big question: What large-scale climate forcings might be influencing climate, and how dynamic are these forcings? It looks like I will need a lot more tea….got milk?

This work would have not been possible without the support of Neil and Amy as my advisors, the expertise of Dr. Baatarbileg Nachin, Dr. Nicole Davi, and field help from Byambagerel Suran, Uyanga Ariya, and Bayra. Oh, and of course Tom!


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