From tree rings to satellites using different tools to study Amazon climate

Transcription

1 From tree rings to satellites using different tools to study Amazon climate Jess Baker Contributors : Dominick Spracklen, Luis Garcia-Carreras, Roel Brienen, Manuel Gloor, Steve Arnold, Arnoud Boom, Julia Tindall, Santiago Clerici, Bruno Cintra, David Neil, Melanie Leng, John Marsham and Wolfgang Buermann

2 Introduction The Amazon is the world s largest drainage basin, covering 7.5 M km 2. Contains ~40% of the world s tropical forest (Araga o et al., 2014). Stores ~17% global terrestrial carbon (Feldpausch et al., 2012). Changes in Amazon climate have impacts for the forest, biodiversity, local inhabitants and global climate.

3 A talk of two halves 1. Proxy climate data: using oxygen isotopes in tree rings to reconstruct Amazon hydrology 2. Remote sensing: investigating Amazon climate using satellite data

4 Part 1 How can tropical tree rings provide insights about past climate?

5 Dormant cambium Active cambium What are tree rings? Tree rings are structures in wood that form as a results of cycles in tree growth. From González et al. (2012), Plant, Cell & Environment Time At the beginning of the growing season, a layer of cells called the cambium starts to divide, forming new xylem and phloem. New wood forms beneath the bark, pushing the bark outwards as the tree grows. As conditions become unfavourable, tree growth slows and eventually stops, and a new ring boundary is formed.

6 Amburana Tree rings in the tropics Tachigali It was originally thought tropical trees didn t form tree rings due to generally favourable growing conditions at low latitudes. Peltogyne Rings can from in response to seasonal drought or seasonal flooding. Couratari Tree rings are a natural climate record but in order to accurately date trees by ring counting need to confirm they are annual.

7 Checking the frequency of tropical tree ring formation 14 C bomb-peak dating can be used to date recent organic material with an accuracy of 1 2 years Peak in atmospheric radiocarbon ( 14 C ) caused by nuclear tests in the 1960s Trees growing during this time take up 14 C during photosynthesis and the signal is preserved in their wood. Hua et al., 2013, Radiocarbon Map of tree ring sample sites in Amazon

8 Some trees regularly form two rings per year! Cedrela trees from Ecuador, Bolivia and Venezuela shown to from annual tree rings, while trees from Suriname formed two rings per year Possibly caused by double rainy season, but there could also be genetic control on growth dynamics Baker et al., 2017, Trees

9 Oxygen isotopes in tree rings There are light and heavy forms of oxygen atom, and these combine with hydrogen to form light and heavy water molecules. Fig. 1 in Roden et al., 2000). First, precipitation (step 1 in Fig. 1.3) determines the isotope composition of the source water available to the tree in the top layers of soil. Next, water uptake and stem transport (steps 2 & 3 in Fig. 1.3) are non-fractionating processes so water entering the leaf has the same isotopic signal as the source/stem water (δ 18 OS; White et al., 1985). In the leaf, preferential transpiration of isotopically light water through the stomata leads to enrichment at the site of evaporation (step 4 in Fig. 1.3; Roden et al., 2000, Barbour et al., 2004). The enrichment of the evaporative pool inside the leaf (δ 18 OE) has been described using the Craig-Gordon model (Eqn. 5), since modified to include the effects of a boundary layer at the leaf surface and diffusion through the stomata (Craig and Gordon, 1965, Dongmann et al., 1974, Isotopes allow water to be traced as it moves through the water cycle. When trees take up water through their roots, the isotope signal of the water can be recorded in tree rings. Figure 1.3 Processes affecting the oxygen isotope composition of cellulose (δ 18 OTR). Numbers indicate precipitation (1), non-fractionating uptake of source water (2), water transport to the leaf (3),

10 Tree ring oxygen isotopes (δ 18 O TR ) in the Amazon Brienen et al., 2012 PNAS Tree ring δ 18 O VSMOW ( ) Óbidos river discharge (10 3 m 3 s -1 ) r = Wetter Dryer Why do δ 18 O TR record variation in precipitation over such a large area?

11 Back trajectory analysis What causes inter-annual variation tree ring oxygen isotopes in the Amazon A trajectory describes the position of an air parcel over time Back trajectory analysis ROTRAJ trajectory model from Reading University (Methven, 1997) ROTRAJ trajectory model (Methven, 1997) ECMWF ERA-Interim reanalysis wind data Calculate daily 10-day trajectories for Calculate daily 10-day air parcel trajectories for Combine trajectories with rainfall data from TRMM Gridded TRMM precipitation data Accumulate precip ( P) along each trajectory during its time over land Accumulate precip ( P) along each trajectory during its time over land Relate δ 18 O TR to P 2010 wet season trajectories 2010 wet season trajectories

12 Precipitation along a sample back trajectory Precip Moving inland

13 Correlations between δ 18 O TR and Precip Correlation coefficient Accumulated precipitation ( Precip) Tree ring δ 18 O Baker et al., 2016, GRL

14 Water vapour transport analysis Baker et al., 2016, GRL Confirms that tree ring δ 18 O reflects Amazon basin moisture balance

15 New Amazon δ 18 O TR records Longest records from Amazon to date, and first to extend beyond instrumental record Good correlation between records, despite coming from sites >1500 km apart with ~2750 m elevation difference Insights on Amazon hydrology over two centuries But long-term trends must still be interpreted with care

16 Using a long tree ring δ 18 O record to question controls on Amazon hydrology Antico and Torres, 2015, GRL Sunspots were reported to influence decadal variation in Amazon River flow

17 Using a long tree ring δ 18 O record to question controls on Amazon hydrology Antico and Torres, 2015, GRL Sunspots were reported to influence decadal variation in Amazon River flow Baker et al., 2018, GRL We tested this hypothesis using a new 200-year long isotope record from Ecuador Amazon discharge (10 4 m 3 s -1 ) δ 18 O TR

18 Using a long tree ring δ 18 O record to question controls on Amazon hydrology Antico and Torres, 2015, GRL Sunspots were reported to influence decadal variation in Amazon River flow Baker et al., 2018, GRL We tested this hypothesis using a new 200-year long isotope record from Ecuador Conclusion: either the relationship between sunspots and Amazon discharge is non-stationary, or the result is coincidental Amazon discharge (10 4 m 3 s -1 ) δ 18 O TR

19 Part 2 Remote sensing: investigating Amazon climate using satellite data

20 LAPSE Earth-observation satellites EO-satellites are designed to monitor the Earth from space This method of monitoring is also known as remote sensing Electromagnetic spectrum Uses reflectance of electromagnetic radiation from Earth to get information about the land surface and/or atmosphere First EO satellites launched in 1964 were the Nimbus series Image of Hurricane Gladys taken in 1964

21 LAPSE Remote sensing instruments can be passive or active Passive sensor Active sensor Forest Bare soil Water Tarmac Urban area Forest Bare soil Water Tarmac Urban area E.g. MODIS, TRMM microwave imager E.g. TRMM precipitation radar

22 LAPSE: Land-Atmosphere interactions and seasonal Precipitation over Brazil: Synthesis of observations and process-based Evaluation Objectives Collate and harmonise satellite observations related to the land surface and the atmosphere Develop new tools for model evaluation Apply to UK and Brazil climate models Provide data and scripts as toolkit for the climate modelling community Learn more about the controls on seasonal precipitation in Brazil and across the tropics

23 Moisture recycling is important in the Amazon Water recycled through transpiring trees is an important driver of tropical precipitation (Spracklen et al., 2012). Moisture recycling Atmospheric transport Evapotranspiration (ET) may be important for wet season initiation in the the southern Amazon (Wright et al, 2017). Precipitation ET patterns are expected to change as plants respond to rising atmospheric CO 2, with consequences for precipitation (e.g. Skinner et al., 2017). We need to measure and understand this key hydrological variable. Evapotranspiration Plant water uptake Runoff

24 Despite it s importance, ET remains a difficult variable to measure ET can be measured from eddy covariance flux towers, though these tend to record sitelevel ET. Where data exist, often only over short timescales (a few years) and/ or discontinuous. No flux towers at all in the western Amazon.

25 Satellite-derived ET products now available Satellite ET products offer spatially comprehensive information over hitherto unmonitored regions. Not a direct measure of ET, but ET as a function of other variables that can be measured by satellites. Being used to monitor global trends in ET and for climate model evaluation. Zhang et al. (2015) Sci. Rep. Important to check consistency of different satellite products.

26 Summary Tropical tree rings can provide valuable information about historical and current climate, especially in regions where instrumental data is limited Meanwhile, satellites can offer spatially comprehensive climate data over recent decades, though products must be chosen with care Combining information from multiple data sources will help us to further understand complex climate feedbacks in remote tropical forest areas

27 Thank you for your attention